Community and Public Sector Union members resumed strike action at airports on Wednesday after postponing the campaign due to the terror attacks in Brussels and the urging of Mr Turnbull.

The protected industrial action is set to last until April 7 with customs and immigration staff walking off the job during morning and evening peak times.

"I would encourage them to continue their discussions with the government, to seek to resolve their industrial disputes in a manner that does not disadvantage our travellers," Mr Turnbull said.

"I can say to you in terms of security however, the security services, the counter-terrorism services in particular at the airports are provided by the Australian Federal Police, and of course, they are taking account of the stoppages in their planning."

But Immigration Minister Peter Dutton said he was not convinced national security would not be compromised by the strike.

"The threat hasn't passed within a couple of days following the Brussels attack," he told ABC Radio. "These rolling strikes aren't welcome and I hope that they come to an end sooner than later."

According to the CPSU, strict national security exemptions will remain in place at international airports during the strike action.

Department of Agriculture staff working in biosecurity will also join the rolling industrial action.

CPSU national secretary Nadine Flood said she expected the industrial action to cause delays for many international travellers but insisted it would not affect national security.

"Our members in Immigration and Border Force and Agriculture and Water Resources will now resume their industrial action, knowing that their campaign never has and never will compromise Australia's national security at airports or anywhere else," she said.

"We can expect some impact on passengers at various airports form these rolling stoppages but the key to stopping these strikes is the Prime Minister.

"The government has given these workers no one to talk to and no way to resolve this dispute other than strike action."

Last week, public service commissioner John Lloyd condemned proposed strike action at international airports as cynical and deliberately designed to cause maximum disruption.

Industrial action at international airports on Thursday:

• Sydney International Airport (midnight-12.15am)
• Melbourne Airport (4am-noon, 4pm-midnight)
• Adelaide Airport (5am-1pm, 4pm-midnight)
• Brisbane International Airport (5am-1pm, 5pm-midnight)
• Cairns International Airport (midnight-1am)
• Townsville Airport (4am-noon)
• Darwin Airport (2am-10am, 1pm-9pm)