The CPSU is making its final arguments this week in the closing stages of a Fair Work battle with the Home Affairs department.

The Community and Public Sector Union (CPSU) will not budge in its primary position on wages and conditions, but was expected to offer the Fair Work Commission an alternative if its arguments are not accepted in full.

“Our position on the key elements of this dispute remains absolutely unchanged," the CPSU said.

The alternative position could see some of the conditions of staff at the former Australian Customs and Border Protection Service treated separately from those in the former Immigration Department.

“This will minimise the risk of a lengthy deliberation that could result in an outcome that impacts on the workers who stand to lose the most,” the union said.

Lawyers for Home Affairs earlier told the Full Bench of the Fair Work Commission that the department's offer to staff represented a balance between competing interests, while maintaining flexibility and taking account of economic conditions.