diff --git a/lib/iris/src/iris/cli/job.py b/lib/iris/src/iris/cli/job.py
index 1f2e1da4e8..c7d602ab10 100644
--- a/lib/iris/src/iris/cli/job.py
+++ b/lib/iris/src/iris/cli/job.py
@@ -30,6 +30,7 @@
     WellKnownAttribute,
     device_variant_constraint,
     infer_preemptible_constraint,
+    preemptible_constraint,
     region_constraint,
     zone_constraint,
 )
@@ -532,6 +533,41 @@ def resolve_multinode_defaults(
     return replicas, coscheduling
 
 
+def build_job_constraints(
+    resources_proto: job_pb2.ResourceSpecProto,
+    tpu_variants: list[str],
+    replicas: int,
+    regions: tuple[str, ...] | None = None,
+    zone: str | None = None,
+    preemptible: bool | None = None,
+) -> list[Constraint]:
+    """Assemble the constraint list for a submitted job.
+
+    An explicit ``preemptible`` value wins over the executor heuristic:
+    ``infer_preemptible_constraint`` short-circuits when any preemptible
+    constraint is already present, so we append the user's choice first.
+    """
+    constraints: list[Constraint] = []
+    if regions:
+        constraints.append(region_constraint(list(regions)))
+    if zone:
+        constraints.append(zone_constraint(zone))
+    if len(tpu_variants) > 1:
+        constraints.append(device_variant_constraint(tpu_variants))
+    if preemptible is not None:
+        constraints.append(preemptible_constraint(preemptible))
+
+    # Executor heuristic: small CPU-only CLI jobs (no accelerators, 1 replica,
+    # CPU ≤ 0.5 cores, RAM ≤ 4 GiB) are auto-tagged as non-preemptible so
+    # coordinators survive spot reclamation. Skipped when the user supplied
+    # --preemptible / --no-preemptible.
+    inferred = infer_preemptible_constraint(resources_proto, replicas, constraints)
+    if inferred is not None:
+        constraints.append(inferred)
+        logger.info("Executor heuristic: auto-tagging job as non-preemptible")
+    return constraints
+
+
 def run_iris_job(
     command: list[str],
     env_vars: dict[str, str],
@@ -553,6 +589,7 @@ def run_iris_job(
     user: str | None = None,
     reserve: tuple[str, ...] | None = None,
     priority: str | None = None,
+    preemptible: bool | None = None,
     token_provider: TokenProvider | None = None,
     submit_argv: list[str] | None = None,
 ) -> int:
@@ -565,6 +602,8 @@ def run_iris_job(
         regions: If provided, restrict the job to workers in these regions.
         zone: If provided, restrict the job to workers in this zone.
         reserve: Reservation specs (e.g., ("4:H100x8", "v5litepod-16")).
+        preemptible: If True/False, force scheduling on (non-)preemptible workers
+            and bypass the executor heuristic. If None (default), the heuristic runs.
 
     Returns:
         Exit code: 0 for success, 1 for failure
@@ -579,22 +618,15 @@ def run_iris_job(
 
     replicas, coscheduling = resolve_multinode_defaults(primary_tpu, gpu, replicas)
 
-    constraints: list[Constraint] = []
-    if regions:
-        constraints.append(region_constraint(list(regions)))
-    if zone:
-        constraints.append(zone_constraint(zone))
-    if len(tpu_variants) > 1:
-        constraints.append(device_variant_constraint(tpu_variants))
-
-    # Executor heuristic: small CPU-only CLI jobs (no accelerators, 1 replica,
-    # CPU ≤ 0.5 cores, RAM ≤ 4 GiB) are auto-tagged as non-preemptible so
-    # coordinators survive spot reclamation.
     resources_proto = resources.to_proto()
-    preemptible = infer_preemptible_constraint(resources_proto, replicas, constraints)
-    if preemptible is not None:
-        constraints.append(preemptible)
-        logger.info("Executor heuristic: auto-tagging job as non-preemptible")
+    constraints = build_job_constraints(
+        resources_proto=resources_proto,
+        tpu_variants=tpu_variants,
+        replicas=replicas,
+        regions=regions,
+        zone=zone,
+        preemptible=preemptible,
+    )
 
     reservation: list[ReservationEntry] | None = None
     if reserve:
@@ -632,6 +664,8 @@ def run_iris_job(
         logger.info(f"Region constraint: {', '.join(regions)}")
     if zone:
         logger.info(f"Zone constraint: {zone}")
+    if preemptible is not None:
+        logger.info(f"Preemptible constraint: {preemptible}")
     if reservation:
         logger.info(f"Reservation: {len(reservation)} entries")
 
@@ -831,6 +865,16 @@ def job() -> None:
     default=None,
     help="Priority band for scheduling (default: interactive). Lower bands run first; batch jobs yield to interactive.",
 )
+@click.option(
+    "--preemptible/--no-preemptible",
+    "preemptible",
+    default=None,
+    help=(
+        "Force scheduling on preemptible (--preemptible) or non-preemptible "
+        "(--no-preemptible) workers. Overrides the executor heuristic. "
+        "Default: heuristic-based (small CPU-only jobs pinned to non-preemptible)."
+    ),
+)
 @click.option(
     "--terminate-on-exit/--no-terminate-on-exit",
     default=True,
@@ -858,6 +902,7 @@ def run(
     extra: tuple[str, ...],
     reserve: tuple[str, ...],
     priority: str | None,
+    preemptible: bool | None,
     terminate_on_exit: bool,
     cmd: tuple[str, ...],
 ):
@@ -907,6 +952,7 @@ def run(
             zone=zone,
             reserve=reserve or None,
             priority=priority,
+            preemptible=preemptible,
             token_provider=ctx.obj.get("token_provider"),
             submit_argv=submit_argv,
         )
diff --git a/lib/iris/tests/cli/test_job.py b/lib/iris/tests/cli/test_job.py
index 7ce01f42b9..4686ae3f32 100644
--- a/lib/iris/tests/cli/test_job.py
+++ b/lib/iris/tests/cli/test_job.py
@@ -9,6 +9,7 @@
 from iris.cli.job import (
     _parse_tpu_alternatives,
     _render_job_summary_text,
+    build_job_constraints,
     build_job_summary,
     build_resources,
     build_tpu_alternatives,
@@ -138,6 +139,52 @@ def test_executor_heuristic_with_region_constraint():
     assert preemptible.values[0].value == "false"
 
 
+# ---------------------------------------------------------------------------
+# build_job_constraints — --preemptible / --no-preemptible wiring (#4540)
+# ---------------------------------------------------------------------------
+
+
+def _preemptible_values(constraints: list[Constraint]) -> list[str]:
+    return [c.values[0].value for c in constraints if c.key == WellKnownAttribute.PREEMPTIBLE]
+
+
+def test_build_job_constraints_preemptible_true_emits_true_constraint():
+    """--preemptible forces a preemptible=true constraint and bypasses the heuristic."""
+    resources_proto = build_resources(tpu=None, gpu=None, cpu=0.5, memory="1GB", disk="5GB").to_proto()
+
+    constraints = build_job_constraints(resources_proto, tpu_variants=[], replicas=1, preemptible=True)
+
+    assert _preemptible_values(constraints) == ["true"]
+
+
+def test_build_job_constraints_preemptible_false_emits_false_constraint():
+    """--no-preemptible forces a preemptible=false constraint even for non-executor jobs."""
+    resources_proto = build_resources(tpu=None, gpu=None, cpu=4.0, memory="16GB", disk="5GB").to_proto()
+
+    constraints = build_job_constraints(resources_proto, tpu_variants=[], replicas=1, preemptible=False)
+
+    assert _preemptible_values(constraints) == ["false"]
+
+
+def test_build_job_constraints_preemptible_none_runs_heuristic():
+    """Default (None) preserves the executor heuristic on small CPU jobs."""
+    resources_proto = build_resources(tpu=None, gpu=None, cpu=0.5, memory="1GB", disk="5GB").to_proto()
+
+    constraints = build_job_constraints(resources_proto, tpu_variants=[], replicas=1, preemptible=None)
+
+    assert _preemptible_values(constraints) == ["false"]
+
+
+def test_build_job_constraints_preemptible_true_overrides_heuristic():
+    """Small CPU jobs normally auto-tag non-preemptible; --preemptible wins."""
+    resources_proto = build_resources(tpu=None, gpu=None, cpu=0.5, memory="1GB", disk="5GB").to_proto()
+
+    constraints = build_job_constraints(resources_proto, tpu_variants=[], replicas=1, preemptible=True)
+
+    # Exactly one preemptible constraint, and it reflects the user's choice.
+    assert _preemptible_values(constraints) == ["true"]
+
+
 # --tpu multi-variant parsing
 # ---------------------------------------------------------------------------