JULIA Gillard’s prime ministership is again under threat, with Labor sources saying government whip Joel Fitzgibbon is now actively canvassing for votes to return Kevin Rudd to the leadership.

The holder of the key government post is normally a bulwark against moves to depose a leader. But sources said he had switched camps some time ago, and was making a case for change to other MPs last week.

Mr Fitzgibbon did not return calls last night but he took to Twitter today to say: ‘‘I thank my colleagues for the publicity but no one does more to support the PM and the government than me!’’

Further comment is being sought from Mr Fitzgibbon. Ms Gillard will give a media conference in Canberra later today.

There is growing despair in Labor ranks about the government’s dismal stocks, and a loss of faith in Ms Gillard’s ability to turn things around. But people close to her in government insist she would not quit the leadership voluntarily.

Some who favour a switch do not want it to happen until the last day of parliamentary sittings in June, when a new leader would have the long winter break to reorganise government and tweak policies.

Government frontbencher Greg Combet said this morning that Labor whip Joel Fitzgibbon needed to answer questions about reports he has switched his support from Julia Gillard to Kevin Rudd.

”I’ve seen the conjecture today so I think probably a few questions might be directed at Joel.”

Ms Gillard won a decisive victory in a caucus ballot against Mr Rudd in February but the vote did not entirely quash leadership speculation.

She will face an angry Labor caucus on Tuesday over her government’s deal to let Gina Rinehart import 1700 foreign workers.

Yesterday she moved to placate union backers with a vow to ”make sure Aussies get jobs first”, announcing the government would create a ”jobs board” to ensure Australians were given the first chance at jobs in the resources sector. The board might involve an online noticeboard where people can post jobs or job wanted listings.

”Companies won’t be able to bring in foreign workers if there is an Australian ready, able and willing to do the work on the jobs board,” she said.

The decision follows anger from unions and Labor MPs after the Minister for Immigration, Chris Bowen, and the Minister for Resources, Martin Ferguson, announced Ms Rinehart would be allowed to import more than 1700 workers to help build Roy Hill, a new iron ore project in the Pilbara. Both ministers backed Mr Rudd in February’s leadership vote, and the Rinehart deal has exposed fresh tensions at the top levels of government.

Ministerial approval has been granted for the deal, but it is understood the contract with Ms Rinehart’s Hancock Prospecting has yet to be negotiated and signed.

Unions warned the deal could ultimately bring in many more foreign workers. The head of the Australian Workers Union, Paul Howes, attacked Mr Bowen’s suggestion the deal had been necessary for Roy Hill to go ahead.

”It’s a $6 billion project,” he said. ”She is worth $29 billion personally. The logic of someone worth $29 billion not being able to secure $6 billion for a project that will be extremely profitable just doesn’t add up. It’s a fundamental misunderstanding of capital raising by the Immigration Minister.”

Ms Gillard did not explicitly endorse the Roy Hill deal yesterday, but argued that, with half a trillion dollars of investment projects in the pipeline, there would be a need for some foreign workers at peak times.

The Opposition Leader, Tony Abbott, seized on reports that suggested Ms Gillard had found out about the deal only on Wednesday and was furious when she was told about it. He declared it was a sign of a government at war with itself.

The union movement yesterday welcomed Ms Gillard’s announcement but said more details of the scheme were needed.

”We are not against skilled migrants … There may be circumstances where it’s needed but [this] is an attempt by some big businesses to hijack migration,” said the head of the Construction, Forestry, Mining and Energy Union, David Noonan.

When Ms Gillard fronts the caucus for the first time since the budget, she will also be forced to address concerns about changes to the single parent payment.