The future of the Coalition's hold on power is at risk with the Federal Government becoming the first to lose a vote on its own legislation in almost 80 years.

Key points: Labor secured the support of most of the crossbench to allow doctors a greater say in refugee medical evacuations

Labor secured the support of most of the crossbench to allow doctors a greater say in refugee medical evacuations Labor and the crossbench had forced a series of measures into a government migration bill

Labor and the crossbench had forced a series of measures into a government migration bill The solicitor-general had warned the proposal might be unconstitutional because it included spending measures

The majority of the crossbench and Labor joined forces in the House of Representatives to pass amendments to give doctors a greater say on refugee medical evacuations.

But Prime Minister Scott Morrison has so far refused to buckle to calls for an early election and insists the Coalition retains the ability to govern.

"Votes will come and they will go, they do not trouble me," he said.

The amendments that passed the House were agreed to by the Senate late last year, after Labor and the crossbench forced a series of measures into a government migration bill.

Labor secured the support of most of the crossbench to win the Lower House vote 75 to 74 on the first sitting day for 2019.

Attorney-General Christian Porter presented legal advice from solicitor-general Stephen Donaghue at the last minute, suggesting the amendments agreed to by the Senate would be unconstitutional.

But Mr Donaghue also pointed out there was case law suggesting the High Court was generally reluctant to intervene in these matters, because it related to sections of the Constitution that gave power to the Parliament to conduct its own affairs.

PM insists election will be held in May

Manager of Opposition business Tony Burke would not rule out moving a vote of no confidence in the Government, to force an early election.

But he said Mr Morrison should reflect on the lost vote and determine if it meant his government had lost the confidence of the House of Representatives.

The Prime Minister immediately rejected that and insisted the election would be in May after the April budget.

"This was not what that vote was about this evening," he said.

"If the Labor Party want to move such a motion, they should feel free to do so and it will fail.

"How do I know that? Because the independents have made that very clear."

Sorry, this video has expired The Opposition says the result doesn't affect confidence in the Government.

People smugglers 'the only winners'

Greens MP Adam Bandt said the crossbench and refugee advocates should claim credit for the outcome.

"By all working together and putting refugees first, we've just made a huge difference," Mr Bandt said.

"The Greens worked with the crossbench and constructively held Labor to account, stopping too much power from remaining in (Home Affairs Minister) Peter Dutton's hands."

But former prime minister Tony Abbott took to Twitter to warn the changes would offer an incentive for people smugglers.

"People smugglers and their customers are the only winners from Labor's weakening of our border protection policies because ample medical treatment offshore and onshore was already available.

"Under Labor, it's get on a boat, get to Nauru, get sick and get to Australia."

Labor's immigration spokesman Shayne Neumann took to Twitter to rebuke the Coalition's attack on his party.

"We just voted to ensure sick and vulnerable people currently on Nauru and Manus Island are able to get the help they need, whilst keeping our stronger border protection arrangements in place," he said.

"This was never about politics. This was about doing the right, decent and humane thing."