British prime minister-in-waiting Andy Burnham backed Home Secretary Shabana Mahmood's controversial immigration crackdown in a parliamentary vote on Monday night.
The wide-ranging bill would make it easier for authorities to deport asylum seekers and impose a "refugee tax" in return for government support.
The government says the legislation is intended to reduce small boat crossings while expanding "safe and legal routes" into the UK. It has been condemned by human rights groups who say it will weaken basic protections for asylum seekers.
The legislation passed its second reading in the House of Commons by 264 votes to 90, with Burnham among the Labour MPs to vote in favour of the bill despite a rebellion by 14 MPs from his own party.
The Makerfield MP's decision to back the bill comes after almost 80 Labour MPs urged him to scale back the reforms, warning that the party is "losing progressive voters" because of Mahmood's hardline approach.
Under the proposals , asylum seekers would be barred from obtaining permanent residence until they pay up to £10,000 for any financial support and accommodation received while waiting for their claims to be processed.
It will also limit the use of the European Convention of Human Rights to prevent deportation and replace immigration judges with a new system of independent adjudicators, which ministers say will speed up decisions but rights advocates say could weaken judicial oversight.
Ahead of the vote, Mahmood introduced new amendments to the bill, which include removing protections that block the deportation of Commonwealth citizens convicted of serious crimes.
Opening the Commons debate, Mahmood said the reforms were necessary to restore public confidence in the asylum system while preserving Britain's commitment to those fleeing war and persecution.
She also said Labour had increased arrests of people smugglers by 55% since taking office, while asylum decisions had reached a 24-year high and removals their highest level in almost a decade.
Refugee charities have criticised the introduction of the "refugee tax" as unfairly penalising asylum seekers who are unable to work until their applications are approved.
Amnesty International has called several aspects of the bill "deeply alarming", including the weakening of protections for families and the proposed overhaul of the appeals system.
The bill has also been met with criticism from Labour backbenchers. Nadia Whittome, the Labour MP for Nottingham East, called the bill "needlessly cruel" in a post on X, while Poplar and Limehouse's Apsana Begum described it as "performative and cruel".
Labour MP Stella Creasy also criticised plans to reassess refugees' status every 30 months, describing them as a "Diet Coke version of refugee status".
The Conservatives also voted against the legislation on Monday, arguing it does not go far enough to curb migration.
Burnham officially secured the Labour leadership on Monday after another 27 MPs backed his candidacy to succeed Keir Starmer. He now has 349 nominations, meaning no other candidates can reach the 81 needed to enter the contest.
The former Manchester mayor is expected to replace Starmer as Labour leader on Friday before becoming prime minister next Monday.
British media reports suggest that he is likely to keep Mahmood in her position as home secretary after he enters Downing Street.