diff --git a/application/applicationextension.inc.php b/application/applicationextension.inc.php
index 7177c3606b..db10eb3823 100644
--- a/application/applicationextension.inc.php
+++ b/application/applicationextension.inc.php
@@ -1914,38 +1914,72 @@ public static function GetClass($oData, $sParamName)
 	public static function GetFieldList($sClass, $oData, $sParamName)
 	{
 		$sFields = self::GetOptionalParam($oData, $sParamName, '*');
-		$aShowFields = array();
-		if ($sFields == '*')
-		{
-			foreach (MetaModel::ListAttributeDefs($sClass) as $sAttCode => $oAttDef)
-			{
-				$aShowFields[$sClass][] = $sAttCode;
-			}
+		return match($sFields) {
+			'*' => self::GetFieldListForClass($sClass),
+			'*+' => self::GetFieldListForParentClass($sClass),
+			default => self::GetLimitedFieldListForClass($sClass, $sFields, $sParamName),
+		};
+	}
+
+	public static function HasRequestedExtendedOutput(string $sFields): bool
+	{
+		return match($sFields) {
+			'*' => false,
+			'*+' => true,
+			default => substr_count($sFields, ':') > 1,
+		};
+	}
+
+	public static function HasRequestedAllOutputFields(string $sFields): bool
+	{
+		return match($sFields) {
+			'*', '*+' => true,
+			default => false,
+		};
+	}
+
+	protected static function GetFieldListForClass(string $sClass): array
+	{
+		return [$sClass => array_keys(MetaModel::ListAttributeDefs($sClass))];
+	}
+
+	protected static function GetFieldListForParentClass(string $sClass): array
+	{
+		$aFieldList = array();
+		foreach (MetaModel::EnumChildClasses($sClass, ENUM_CHILD_CLASSES_ALL) as $sRefClass) {
+			$aFieldList = array_merge($aFieldList, self::GetFieldListForClass($sRefClass));
 		}
-		elseif ($sFields == '*+')
+		return $aFieldList;
+	}
+
+	protected static function GetLimitedFieldListForSingleClass(string $sClass, string $sFields, string $sParamName): array
+	{
+		$aFieldList = [$sClass => []];
+		foreach (explode(',', $sFields) as $sAttCode)
 		{
-			foreach (MetaModel::EnumChildClasses($sClass, ENUM_CHILD_CLASSES_ALL) as $sRefClass)
+			$sAttCode = trim($sAttCode);
+			if (($sAttCode != 'id') && (!MetaModel::IsValidAttCode($sClass, $sAttCode)))
 			{
-				foreach (MetaModel::ListAttributeDefs($sRefClass) as $sAttCode => $oAttDef)
-				{
-					$aShowFields[$sRefClass][] = $sAttCode;
-				}
+				throw new Exception("$sParamName: invalid attribute code '$sAttCode'");
 			}
+			$aFieldList[$sClass][] = $sAttCode;
 		}
-		else
-		{
-			foreach (explode(',', $sFields) as $sAttCode)
-			{
-				$sAttCode = trim($sAttCode);
-				if (($sAttCode != 'id') && (!MetaModel::IsValidAttCode($sClass, $sAttCode)))
-				{
-					throw new Exception("$sParamName: invalid attribute code '$sAttCode'");
-				}
-				$aShowFields[$sClass][] = $sAttCode;
-			}
+		return $aFieldList;
+	}
+
+	protected static function GetLimitedFieldListForClass(string $sClass, string $sFields, string $sParamName): array
+	{
+		if (!str_contains($sFields, ':')) {
+			return self::GetLimitedFieldListForSingleClass($sClass, $sFields, $sParamName);
 		}
 
-		return $aShowFields;
+		$aFieldList = [];
+		$aFieldListParts = explode(';', $sFields);
+		foreach ($aFieldListParts as $sClassFields) {
+			list($sSubClass, $sSubClassFields) = explode(':', $sClassFields);
+			$aFieldList = array_merge($aFieldList, self::GetLimitedFieldListForSingleClass(trim($sSubClass), trim($sSubClassFields), $sParamName));
+		}
+		return $aFieldList;
 	}
 
 	/**
diff --git a/core/restservices.class.inc.php b/core/restservices.class.inc.php
index 3ad0ae74e3..c4198bd076 100644
--- a/core/restservices.class.inc.php
+++ b/core/restservices.class.inc.php
@@ -503,8 +503,8 @@ public function ExecOperation($sVersion, $sVerb, $aParams)
 		case 'core/get':
 			$sClass = RestUtils::GetClass($aParams, 'class');
 			$key = RestUtils::GetMandatoryParam($aParams, 'key');
+			$sShowFields = RestUtils::GetOptionalParam($aParams, 'output_fields', '*');
 			$aShowFields = RestUtils::GetFieldList($sClass, $aParams, 'output_fields');
-			$bExtendedOutput = (RestUtils::GetOptionalParam($aParams, 'output_fields', '*') == '*+');
 			$iLimit = (int)RestUtils::GetOptionalParam($aParams, 'limit', 0);
 			$iPage = (int)RestUtils::GetOptionalParam($aParams, 'page', 1);
 
@@ -528,7 +528,8 @@ public function ExecOperation($sVersion, $sVerb, $aParams)
             }
 			else
 			{
-                                if (!$bExtendedOutput && RestUtils::GetOptionalParam($aParams, 'output_fields', '*') != '*') 
+
+                                if (!RestUtils::HasRequestedAllOutputFields($sShowFields))
                                 {
                                         $aFields = $aShowFields[$sClass];
                                         //Id is not a valid attribute to optimize
@@ -542,7 +543,7 @@ public function ExecOperation($sVersion, $sVerb, $aParams)
                                 
 				while ($oObject = $oObjectSet->Fetch())
 				{
-					$oResult->AddObject(0, '', $oObject, $aShowFields, $bExtendedOutput);
+					$oResult->AddObject(0, '', $oObject, $aShowFields, RestUtils::HasRequestedExtendedOutput($sShowFields));
 				}
 				$oResult->message = "Found: ".$oObjectSet->Count();
 			}
diff --git a/tests/php-unit-tests/unitary-tests/webservices/RestTest.php b/tests/php-unit-tests/unitary-tests/webservices/RestTest.php
index 6b1c6848a3..70e9bd0a8b 100644
--- a/tests/php-unit-tests/unitary-tests/webservices/RestTest.php
+++ b/tests/php-unit-tests/unitary-tests/webservices/RestTest.php
@@ -142,6 +142,58 @@ public function testCoreApiGet(){
 		$this->assertJsonStringEqualsJsonString($sExpectedJsonOuput, $sJSONOutput);
 	}
 
+	public function testCoreApiGetWithUnionAndDifferentOutputFields(){
+		// Create ticket
+		$description = date('dmY H:i:s');
+		$oUserRequest = $this->CreateSampleTicket($description);
+		$oChange = $this->CreateSampleTicket($description, 'Change');
+		$iUserRequestId = $oUserRequest->GetKey();
+		$sUserRequestRef = $oUserRequest->Get('ref');
+		$iChangeId = $oChange->GetKey();
+		$sChangeRef = $oChange->Get('ref');
+
+		$sJSONOutput = $this->CallCoreRestApi_Internally(<<<JSON
+{
+   "operation": "core/get",
+   "class": "Ticket",
+   "key": "SELECT UserRequest WHERE id=$iUserRequestId UNION SELECT Change WHERE id=$iChangeId",
+   "output_fields": "Ticket:ref;UserRequest:ref,status,origin;Change:ref,status,outage"
+}
+JSON);
+
+		$sExpectedJsonOuput = <<<JSON
+{
+    "code": 0,
+    "message": "Found: 2",
+    "objects": {
+    	"Change::$iChangeId": {
+            "class": "Change",
+            "code": 0,
+            "fields": {
+            	"outage": "no",
+                "ref": "$sChangeRef",
+                "status": "new"
+            },
+            "key": "$iChangeId",
+            "message": ""
+        },
+        "UserRequest::$iUserRequestId": {
+            "class": "UserRequest",
+            "code": 0,
+            "fields": {
+            	"origin": "phone",
+                "ref": "$sUserRequestRef",
+                "status": "new"
+            },
+            "key": "$iUserRequestId",
+            "message": ""
+        }
+    }
+}
+JSON;
+		$this->assertJsonStringEqualsJsonString($sExpectedJsonOuput, $sJSONOutput);
+	}
+
 	public function testCoreApiCreate()
 	{
 		// Create ticket
@@ -253,9 +305,9 @@ public function testCoreApiDelete()
 	//
 	////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
-	private function CreateSampleTicket($description)
+	private function CreateSampleTicket($description, $sType = 'UserRequest')
 	{
-		$oTicket = $this->createObject('UserRequest', [
+		$oTicket = $this->createObject($sType, [
 			'org_id' => $this->getTestOrgId(),
 			"title" => "Houston, got a problem",
 			"description" => $description
diff --git a/tests/php-unit-tests/unitary-tests/webservices/RestUtilsTest.php b/tests/php-unit-tests/unitary-tests/webservices/RestUtilsTest.php
new file mode 100644
index 0000000000..d62ae3af7c
--- /dev/null
+++ b/tests/php-unit-tests/unitary-tests/webservices/RestUtilsTest.php
@@ -0,0 +1,101 @@
+<?php
+
+namespace Combodo\iTop\Test\UnitTest\Webservices;
+
+use Combodo\iTop\Test\UnitTest\ItopDataTestCase;
+use MetaModel;
+use RestUtils;
+use Ticket;
+use UserRequest;
+
+
+class RestUtilsTest extends ItopDataTestCase
+{
+	public function testGetFieldListForSingleClass(): void
+	{
+		$aList = RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => 'ref,start_date,end_date'], 'output_fields');
+		$this->assertSame([Ticket::class => ['ref', 'start_date', 'end_date']], $aList);
+	}
+
+	public function testGetFieldListForSingleClassWithInvalidFieldNameFails(): void
+	{
+		$this->expectException(\Exception::class);
+		$this->expectExceptionMessage('output_fields: invalid attribute code \'something\'');
+		$aList = RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => 'ref,something'], 'output_fields');
+		$this->assertSame([Ticket::class => ['ref', 'start_date', 'end_date']], $aList);
+	}
+
+	public function testGetFieldListWithAsteriskOnParentClass(): void
+	{
+		$aList = RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => '*'], 'output_fields');
+		$this->assertArrayHasKey(Ticket::class, $aList);
+		$this->assertContains('operational_status', $aList[Ticket::class]);
+		$this->assertNotContains('status', $aList[Ticket::class], 'Representation of Class Ticket should not contain status, since it is defined by children');
+	}
+
+	public function testGetFieldListWithAsteriskPlusOnParentClass(): void
+	{
+		$aList = RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => '*+'], 'output_fields');
+		$this->assertArrayHasKey(Ticket::class, $aList);
+		$this->assertArrayHasKey(UserRequest::class, $aList);
+		$this->assertContains('operational_status', $aList[Ticket::class]);
+		$this->assertContains('status', $aList[UserRequest::class]);
+	}
+
+	public function testGetFieldListForMultipleClasses(): void
+	{
+		$aList = RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => 'Ticket:ref,start_date,end_date;UserRequest:ref,status'], 'output_fields');
+		$this->assertArrayHasKey(Ticket::class, $aList);
+		$this->assertArrayHasKey(UserRequest::class, $aList);
+		$this->assertContains('ref', $aList[Ticket::class]);
+		$this->assertContains('end_date', $aList[Ticket::class]);
+		$this->assertNotContains('status', $aList[Ticket::class]);
+		$this->assertContains('status', $aList[UserRequest::class]);
+		$this->assertNotContains('end_date', $aList[UserRequest::class]);
+	}
+
+	public function testGetFieldListForMultipleClassesWithInvalidFieldNameFails(): void
+	{
+		$this->expectException(\Exception::class);
+		$this->expectExceptionMessage('output_fields: invalid attribute code \'something\'');
+		RestUtils::GetFieldList(Ticket::class, (object) ['output_fields' => 'Ticket:ref;UserRequest:ref,something'], 'output_fields');
+	}
+
+	/**
+	 * @dataProvider extendedOutputDataProvider
+	 */
+	public function testIsExtendedOutputRequest(bool $bExpected, string $sFields): void
+	{
+		$this->assertSame($bExpected, RestUtils::HasRequestedExtendedOutput($sFields));
+	}
+
+	/**
+	 * @dataProvider allFieldsOutputDataProvider
+	 */
+	public function testIsAllFieldsOutputRequest(bool $bExpected, string $sFields): void
+	{
+		$this->assertSame($bExpected, RestUtils::HasRequestedAllOutputFields($sFields));
+	}
+
+	public function extendedOutputDataProvider(): array
+	{
+		return [
+			[false, 'ref,start_date,end_date'],
+			[false, '*'],
+			[true, '*+'],
+			[false, 'Ticket:ref'],
+			[true, 'Ticket:ref;UserRequest:ref'],
+		];
+	}
+
+	public function allFieldsOutputDataProvider(): array
+	{
+		return [
+			[false, 'ref,start_date,end_date'],
+			[true, '*'],
+			[true, '*+'],
+			[false, 'Ticket:ref'],
+			[false, 'Ticket:ref;UserRequest:ref'],
+		];
+	}
+}