diff --git a/policy/diamond/policy/blueapi/blueapi.rego b/policy/diamond/policy/blueapi/blueapi.rego
index bf2df8a..f939800 100644
--- a/policy/diamond/policy/blueapi/blueapi.rego
+++ b/policy/diamond/policy/blueapi/blueapi.rego
@@ -1,6 +1,9 @@
 package diamond.policy.blueapi
 
+import data.diamond.policy.admin
+import data.diamond.policy.session
 import data.diamond.policy.token
+
 import rego.v1
 
 default tiled_service_account_for_beamline := false
@@ -10,3 +13,15 @@ tiled_service_account_for_beamline if {
 	"tiled-writer" in token.claims.aud
 	not token.claims.fedid
 }
+
+default write_to_beamline_visit := false
+
+write_to_beamline_visit if {
+	session.write_to_beamline_visit
+}
+
+# Service account check
+write_to_beamline_visit if {
+	input.beamline == token.claims.beamline
+	input.beamline == session.beamline
+}
diff --git a/policy/diamond/policy/blueapi/blueapi_test.rego b/policy/diamond/policy/blueapi/blueapi_test.rego
index 73e94a4..474eec8 100644
--- a/policy/diamond/policy/blueapi/blueapi_test.rego
+++ b/policy/diamond/policy/blueapi/blueapi_test.rego
@@ -3,6 +3,75 @@ package diamond.policy.blueapi_test
 import data.diamond.policy.blueapi
 import rego.v1
 
+diamond_data := {
+	"subjects": {
+		"alice": {
+			"permissions": [],
+			"proposals": [1],
+			"sessions": [],
+		},
+		"bob": {
+			"permissions": ["b07_admin"],
+			"proposals": [],
+			"sessions": [11],
+		},
+		"carol": {
+			"permissions": ["super_admin"],
+			"proposals": [],
+			"sessions": [],
+		},
+		"desmond": {
+			"permissions": [],
+			"proposals": [2],
+			"sessions": [13],
+		},
+		"edna": {
+			"permissions": [],
+			"proposals": [2],
+			"sessions": [13, 14],
+		},
+		"oscar": {
+			"permissions": [],
+			"proposals": [],
+			"sessions": [],
+		},
+	},
+	"sessions": {
+		"11": {
+			"beamline": "i03",
+			"proposal_number": 1,
+			"visit_number": 1,
+		},
+		"12": {
+			"beamline": "b07",
+			"proposal_number": 1,
+			"visit_number": 2,
+		},
+		"13": {
+			"beamline": "b07",
+			"proposal_number": 2,
+			"visit_number": 1,
+		},
+		"14": {
+			"beamline": "b07",
+			"proposal_number": 2,
+			"visit_number": 2,
+		},
+	},
+	"proposals": {
+		"1": {"sessions": {
+			"1": 11,
+			"2": 12,
+		}},
+		"2": {"sessions": {
+			"1": 13,
+			"2": 14,
+		}},
+	},
+	"beamlines": {"i03": {"sessions": [11]}, "b07": {"sessions": [12, 13, 14]}},
+	"admin": {"b07_admin": ["b07"]},
+}
+
 test_service_account_if_beamline_matches if {
 	blueapi.tiled_service_account_for_beamline with input as {"beamline": "i22"}
 		with data.diamond.policy.token.claims as {"beamline": "i22", "aud": ["tiled-writer"]}
@@ -22,3 +91,23 @@ test_not_service_account_if_fedid_present if {
 	not blueapi.tiled_service_account_for_beamline with input as {"beamline": "i22"}
 		with data.diamond.policy.token.claims as {"beamline": "i22", "aud": ["tiled-writer"], "fedid": "abc12345"}
 }
+
+# service account UDC path
+
+test_write_to_beamline_visit_service_account if {
+	blueapi.write_to_beamline_visit with data.diamond.data as diamond_data
+		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
+		with data.diamond.policy.token.claims as {"beamline": "i03"}
+}
+
+test_write_to_beamline_visit_service_account_wrong_beamline if {
+	not blueapi.write_to_beamline_visit with data.diamond.data as diamond_data
+		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
+		with data.diamond.policy.token.claims as {"beamline": "b07"}
+}
+
+test_write_to_beamline_visit_service_account_nonexistent_beamline if {
+	not blueapi.write_to_beamline_visit with data.diamond.data as diamond_data
+		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
+		with data.diamond.policy.token.claims as {"beamline": "i99"}
+}