The move, which is expected to cause delays to travellers on April 18, comes as the union, the CPSU, and the Immigration Department battle in the industrial tribunal over the right of Border Force workers to strike.

The union announced on Friday that the bio-security public servants, working for the Agriculture department, would strike at airports, sea ports and other "key sites" on Monday, April 18.

The CSPU says the strike will go ahead, regardless of the outcome of the action in the Fair Work Commission which banned Border Force officials from striking after the Immigration Department which employs them claimed the strikers were endangering national security.

The April 18 action was announced after Agriculture stood down or docked pay from its public servants already involved in limited stoppages, with the department arguing its employees had been given fair warning of the consequences of striking.

The department has been contacted for comment.

Agriculture's workforce has now rejected three workplace agreement offers put together under the government's tough public service bargaining policy, with fears that key conditions and entitlements are to be cut.

CPSU Deputy Secretary Melissa Donnelly said the April 18 action was being planned "to demonstrate (Agriculture employees') growing frustration with the department and the government over what has been a two-year struggle to keep their rights and conditions".

"This latest strike action shows workers in the Department of Agriculture won't be intimidated, either by the harsh stand-down tactics employed by their bosses or the Department of Immigration's ongoing attempts to stop industrial action using the Fair Work Commission," the union official said.

"We're advising passengers arriving on international flights and people interacting with Agriculture in other areas such as freight to be prepared for some disruption."