Commitments to workers' rights in Boris Johnson's Brexit deal have been condemned as "meaningless" amid fears employers could be left free to exploit their staff if UK law diverges from the EU's in years to come.
It comes just hours after the prime minister unveiled the 110-page Withdrawal Agreement Bill (WAB), with No 10 intending to push it through the House of Commons in just three days.
Key to securing its successful passage, Mr Johnson must rely on Labour MPs to vote with the government after the Democratic Unionist Party ruled out supporting the prime minister's Brexit deal.
Frances O'Grady, the chair of the Trade Union Congress (TUC), however, described the proposals in the so-called WAB as "meaningless", adding: "We still have no legally binding guarantee that UK rights will keep pace with EU minimum standards.
"Don't be conned. This is a bad deal for working people and MPs should vote against it," she said.
The legislation sets out that workers' rights currently derived from EU law will continue to be applied in the UK, including the the Working Time Directive and the Agency Workers' Regulations.
But in the longer term, it adds that after the Brexit transition period ministers will be required to give parliament the opportunity to "consider any future changes to EU law that change EU workers' rights" where they diverge with from UK standards.
In an article for The Times, Ms O'Grady added: "No one should be fooled by Boris Jonhson, Michael Gove and Dominic Raab's last-minute attempts to present themselves as workers' champions.
"They've negotiated a bad deal that would destroy jobs and sell our hard-won rights down the river."
She continued: "Most importantly, these proposals sit alongside a Brexit deal that gives government a licence to shred workers' rights."
"Throughout the Brexit process, trade unions have called for an internationally binding legal guarantee that existing rights will be protected, and that workers’ rights in the UK will at least keep pace with those across the EU in the future.
"The prime minister’s rushed-out paper promises are no substitute for a guarantee, especially given this government is so hostile to scrutiny, and this prime minister is so willing to go back on his word."
Tweeting a picture of the section of the bill of "protection for workers' rights", the Scottish first minister and SNP leader Nicola Sturgeon said: "This is the so-called protection for workers' rights – government must make a statement on whether or not a future bill erodes workers' rights."
Labour leader Jeremy Corbyn added: "Labour opposes Johnson's sell-out deal and will seize every opportunity to safeguard workers' rights, protect our economy and ensure the people are given the Final Say."
Pressed on why there was a lack of guarantees on workers' rights in the legislation, Robert Jenrick, the housing secretary, told Radio 4's Today programme it would be for MPs to decide in the future.
"We are saying that parliament will decide, and that's the point of taking back control, isn't it?" he said. "Trusting parliament to make important decisions on workers' rights or the environment.'
He added the government was likely to improve rights "further and faster" than the European Union. "We have no intention of falling behind Europe and I suspect we are going to go further and faster than our European friends," he said.