Andrew Hastie has quit the Coalition frontbench over a dispute on immigration policy, increasing pressure on Sussan Ley’s leadership.

Hastie said on Friday night that he was resigning as the shadow home affairs minister after weeks of posturing and his refusal to see Ley during her visit to Western Australia this week.

The conservative Liberal MP has openly discussed his ambitions to lead the party in the future, and his resignation will be seen as a possible attempt to oust Ley as opposition leader.

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Hastie blamed his resignation on a charter letter from Ley, outlining her expectations of him as a member of the opposition frontbench, and stating he would not be involved in formulation of immigration policy.

“The leader has made it clear that the shadow home affairs minister won’t lead the Coalition’s response to immigration matters or develop the Coalition’s immigration strategy,” Hastie said in a statement.

“On this basis, I made the decision that I was not able to continue in this role and remain silent on immigration.

“It is a well established standard in the Westminster system that, if a member of the shadow cabinet is unwilling to live by the convention of solidarity, they must depart to the backbench.”

Hastie’s resignation follows Ley’s move last month to sack outspoken Liberal senator Jacinta Nampijinpa Price. Price, who is aligned with Ley’s leadership rival Angus Taylor, declined to express confidence in her leadership.

Hastie has the backing of conservative Liberals and party elders including the former prime minister Tony Abbott.

Hastie said however that Ley should be allowed to continue as opposition leader.

“Sussan deserves the opportunity to lead, unencumbered by interventions from shadow cabinet colleagues, especially as the Coalition builds out a policy platform for the 2028 election,” he said.

“I am grateful for the opportunity to have served as the shadow home affairs minister, and I wish Sussan and the shadow cabinet every success in this term.”

Hastie is due to hold a press conference in Perth on Saturday morning. He wrote to supporters just as a statement announcing his resignation was released, saying he would speak his mind from the backbench.

Ley said she expected solidarity from shadow ministers in public commentary and on parliamentary votes and that Hastie had indicated he would be unable to provide such a guarantee.

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“This expectation is not new and is a fundamental feature of our Westminster system of government. Compliance with this convention has always been a prerequisite for serving in both cabinet and shadow cabinet,” she said.

“I thanked Mr Hastie for his service, and assured him he would continue to be a very valued part of my Coalition team.”

Earlier this week, Ley said she did not believe Hastie was after her job, subtly rebuffing his claims that immigration levels were making Australians feel like “strangers in our own home”.

She declined to endorse Hastie’s comment, instead blaming the government for not building the infrastructure needed to cope with a growing population.

The Western Australian MP has used social media to openly discuss policy matters and to warn that the Liberal party could “die” as a political movement if it does not commit to curb net overseas migration, which he blamed for the housing crisis.

He has also been outspoken on the issue of net zero by 2050 policies, calling the setting a “straitjacket” on the economy. Ley has insisted opposition policy should be carefully reviewed before the next election, despite Nationals and conservative Liberals pushing for net zero to be dumped.

She said changes to the frontbench would be announced soon and named Liberal senator James Paterson to serve as the acting shadow minister for home affairs.