Sir Keir Starmer has pledged to cut levels of net migration to the UK if his party wins the general election.
The Labour leader said he would introduce new laws to train British workers to plug skills gaps in the job market and strengthen anti-exploitation laws.
He did not put a timeframe or a target figure on his promise, but told the Sun on Sunday: "Mark my words, a future Labour government will bring down net migration."
The Conservatives, who recently introduced measures designed to cut the number of arrivals to the UK, said "no one believes Keir Starmer is serious about tackling immigration".
Explaining why Labour did not want to set a target, shadow home secretary Yvette Cooper said previous ones set by the Conservatives had been missed and “discredited the whole system”.
Speaking on OceanNewsUK One's Sunday with Laura Kuenssberg, she also argued that other factors would produce variations “from one year to another," citing the pandemic and the UK's decision to accept Ukrainian refugees as recent examples.
But she said Labour wanted to see "significant changes in place” across the economy to reduce reliance on overseas workers.
Announcing the new policy to the Sun, Sir Keir declared: "If you trust me with the keys to No 10 I will make you this promise: I will control our borders and make sure British businesses are helped to hire Brits first."
The aim would be for the country to be "less reliant on migration by training more UK workers", Sir Keir added.
He said "the Tories have repeatedly broken their promises to bring down net migration".
Last year, net migration - the number of people coming to the UK, minus the number leaving - was 685,000, figures from the Office for National Statistics (ONS) show.
Earlier this year, the government introduced new laws designed to cut immigration numbers.
They included increasing the minimum salary requirement for some skilled work visas by nearly 50%, as well as increasing the salary requirement for skilled workers to bring family dependents with them.
When that policy was announced, shadow home secretary Yvette Cooper said while net migration "should come down", the Conservatives were "failing to introduce more substantial reforms that link immigration to training and fair pay requirements in the UK, meaning many sectors will continue to see rising numbers of work visas because of skills shortages".
Sir Keir has previously described net migration levels as "shockingly high" and this fresh commitment is likely to be seen as an attempt to appeal to traditional Conservative voters.
Under the proposed policy, bosses who breach employment law, such as by paying below minimum wage, could be banned from hiring foreigners.
A spokesperson for the Conservative Party said the new Labour policy announced on Sunday was a "U-turn" on Sir Keir's principles.
"This is the man who called all immigration laws racist and voted against tougher border controls 139 times," the spokesperson said.
Alison Thewliss, from the SNP, said: “Instead of coming forward with policies based on Scotland’s needs, Keir Starmer and Rishi Sunak are both amping up the far-right belief that migrants are to blame for all of our problems - but it’s not migrants, it’s Westminster."
"From our care sector and our NHS to our economy, the cruel immigration policies that both the Tories and Keir Starmer’s Labour have now adopted directly harm Scotland," she said.
A spokesperson for the Liberal Democrats said: "It’s clear the Conservatives have failed on immigration and broken every promise they’ve ever made."
