Perth-based cabinet ministers Julie Bishop and Mathias Cormann say the party is being realistic about its chances in choosing not to run candidates.

However WA Liberal senator Dean Smith has broken ranks.

"It's like the Fremantle Dockers deciding not to turn up at Saturday's game against the West Coast Eagles because they don't think they'll win," he told ABC TV.

"You diminish fan loyalty and you don't set yourself up for the premiership in the following seasons."

The foreign minister said even when the Liberals won 57 per cent of the statewide primary vote in WA, Perth voted for Labor.

"The seat of Perth is a Labor stronghold... we've got to be realistic," Ms Bishop told reporters in Perth on Monday.

"We're being pragmatic about it, we're having to fight by-elections across Australia as a result of Bill Shorten misleading Australians about the citizenship of his members."

Labor MP Tim Hammond resigned from his Perth seat for family reasons, while four other MPs resigned after a High Court ruling meant they were ineligible to be elected in 2016.

Senator Cormann said running candidates would be pointless.

"You always ought to concentrate and prioritise your resources into those contests where you're most likely to be successful," he said in Perth.

State Director of the WA Liberal Party Sam Calabrese issued a statement on Saturday saying the party would focus on contesting the state by-election for the seat of Darling Range but field candidates for Perth and Fremantle in the "real" federal election next year.

WA Opposition Leader Mike Nahan said the seats were "real firm Labor" despite the party's margin in the seat of Perth being only 3.3 per cent.

"They've decided to reserve all their best people and funds for the real season rather than pre-season," Dr Nahan told reporters.

"And I think that's a logical decision and an appropriate one."

A date has yet to be set for the by-elections.

Australian Associated Press