Ed Miliband has promised that employers exploiting migrant workers will face jail under a Labour government.
The Labour leader, in a major speech on immigration in Great Yarmouth, said his administration would make it a criminal offence to undercut pay or conditions by exploiting migrant workers.
"We are serving notice on employers who bring workers here under duress or on false terms and pay them significantly lower wages, with worse terms and conditions," Miliband said.
"This new criminal offence will provide protection to everyone. It will help ensure that, when immigrants work here, they do not face exploitation themselves and rogue employers are stopped from undercutting the terms and conditions of everyone else."
Miliband also reaffirmed his position that there need to be "fair rules" for immigrants who are entering the UK and seeking benefits.
"Fair rules mean that entitlement to benefits needs to be earned. That is why we have already published proposals to prevent people coming here claiming benefit for at least two years," the Labour leader said.
"Fair rules means people integrating into communities and learning English.
"But it isn't just the benefits system that needs to be fair. It is the workplace too. We know that so many workplaces are so far from being fair today. And that is especially true in many workplaces with a large number of employees who have come from overseas."
Miliband claimed he has heard of people having their wages stolen by rogue employers and having to live in "the most appalling conditions".
"These practices have an effect on local workers too. Because when people can be exploited for low wages or endangered at work, it drags the whole system down, undercutting the pay and conditions of people here," he added.
As well as addressing the issue of immigration, Miliband restated that a Labour government would keep the UK inside of the European Union (EU) – in contrast to the Conservative's policy of holding a referendum on the issue in 2017 and Ukip's stance of leaving the economic and political union.
The speech came amid reports Labour MPs have been told not to campaign on the issue ahead of the 2015 general election.
The Daily Telegraph obtained a private strategy document circulated by party bosses, instructing MPs to "move the conversation on" if voters express concerns over border controls and talk about healthcare or housing.
But Labour hit back at the report and Rachel Reeves, the shadow work and pensions secretary, told BBC Radio 4's Today programme that the paper had taken the document "out of context".