The Morrison government plans to slash $150 million from the Home Affairs staff budget, prompting fears the national security agency intends to axe thousands of workers.

The department confirmed the spending cut was due to "ceasing measures" but would not say what parts of its operations would be discontinued.

Home Affairs Minister Peter Dutton on Thursday promoted the government's record on border protection and said the Coalition's policies would remain unchanged if re-elected on May 18.

The Department of Home Affairs, including the Australian Border Force, has attributed a projected $150 million fall in wages spending to unspecified "ceasing measures". Credit:Marina Neil

However figures buried in last month's federal budget show the department's employee benefits payments, which include staff wages and salaries, will drop by $150 million in the year to June 2021. The money is not restored over the forward estimates.