Senior Turnbull Government ministers have endorsed the Liberal Party's decision not to contest two federal WA seats in upcoming by-elections, saying it would have been a waste of "limited resources".

The Liberals will not run candidates in the federal seats of Fremantle and Perth following the resignations of Labor's Tim Hammond and Josh Wilson.

Mr Hammond said the toll the job was taking on his family was too great, while Mr Wilson stood down in the wake of the High Court's latest ruling on dual citizenship.

Federal Finance Minister Mathias Cormann backed the move to not run Liberal candidates in either seat.

"The Liberal Party … always has to make judgements on prioritising limited resources and it is never a good idea to just waste money on a contest you are unlikely to win," Senator Cormann said.

He said it was virtually impossible for the party to win either seat.

Senator Cormann said resources were instead going into the state seat of Darling Range, made vacant by the resignation of disgraced former Labor MP Barry Urban.

Mathias Cormann says the Liberals need to prioritise limited resources. ( ABC News: Jed Cooper )

Mr Urban quit the WA Parliament after facing expulsion for repeatedly lying about his past and is now facing a criminal investigation.

Senator Cormann said the Liberals were in a position to send Labor a message in Darling Range because of the disgraceful circumstance behind Mr Urban's departure.

Liberals will not be 'distracted': Cash

His colleague, federal Minister for Jobs and Innovation Michaelia Cash, backed the sentiment, saying she was confident the party could win back the seat of Darling Range.

"They've said they're not going to be distracted by these by-elections and we're very much going to be focusing on the state seat [which] was previously held by the Liberal Party," Senator Cash said.

"We have a very good chance of winning that seat."

Foreign Affairs Minister Julie Bishop said the party was being "realistic".

Sorry, this video has expired 'We have limited resources' Julie Bishop on the Liberal Party not contesting the by-elections in Perth, Fremantle

"Even when we had 57 per cent of the two-party preferred vote, the electors of Perth still returned a Labor member to Perth," Ms Bishop said.

"So we're being pragmatic about it."

State Opposition Leader Mike Nahan said he thought the decision was logical.

"There's going to be a real game, that is an election in less than a year, and I think they've decided to reserve all their best people and funds for the real season, rather than the pre-season."

But not everyone inside the Liberal Party was happy with the decision.

Liberal Senator Dean Smith said his party was giving Labor a "free kick" in Perth and Fremantle and criticised its decision to vacate the field.

"It's like the Fremantle Dockers deciding not to turn up at Saturday's match with the West Coast Eagles because they think they won't win," he told the ABC.

"The consequence of that is you diminish fan loyalty and you don't set yourself up for the premiership in the next season."

Party 'running scared' from electoral fight

But WA Deputy Premier Roger Cook claimed the party was "running scared" and had abandoned voters.

"I think it's an extraordinary situation where the Liberals have decided to simply abandon the field and simply abandon their voters in (Fremantle and Perth)," Mr Cook said.

"I am not sure why they're running scared but clearly they don't want to be tested by the people of Western Australia."

The decision not to field federal candidates comes despite the Liberals losing Perth by less than 4 per cent at the last federal election.

Labor won Fremantle with a 7.52 per cent margin, taking it out of marginal seat territory.