Ministers including Boris Johnson and Michael Gove are plotting to scrap the working time directive, according to numerous media reports. This is a crucial piece of EU law that protects working people – and which working people were promised would still apply after Brexit.

If Johnson and Gove succeed, 7 million workers could lose their guaranteed legal right to paid holidays. That includes nearly 5 million women and many workers on part-time and zero-hours contracts.

Stripped of the laws that restrain them, bad bosses could force their staff to work excessive hours, far above the current limit of 48 hours a week. Lunch and rest breaks would be under threat too, as would health and safety protections for night workers.

Workers in sectors like health and transport are more likely to make dangerous mistakes if they’re overworked and exhausted – so we should all worry about the impact of taking away these legal rights.

Theresa May’s promise is being put to the test. Will she keep her word? Or is she a hostage to the hard Brexiteers in her cabinet?

Since these rules were introduced, in 1998, they have transformed working life – and family life too. Everyone deserves the guarantee of time off to rest, relax and spend with family and friends.

And it’s not just about the working time directive. If Johnson, Gove and their allies win on this, they’ll surely be emboldened to come after other hard-won rights. Those secured by the EU include parental leave, time off for family emergencies, equal pay for women and equal rights for part-time, fixed-term and agency workers.

During the referendum campaign, Vote Leave promised Britain’s workers that their rights from the EU would be safe after Brexit. In the year and a half since, the prime minister has repeatedly stressed her desire to “protect and extend” workers’ rights – including in the Conservative manifesto.

So Theresa May’s promise is now being put to the test. Will she keep her word? Or is she a hostage to the hard Brexiteers in her cabinet?

That’s why I’m so concerned by the prospect of a Brexit deal modelled on the Ceta deal between the EU and Canada. David Davis has called Ceta “the perfect starting point” for trade talks. But Ceta puts the rights of corporations and foreign investors ahead of those of working people.

Worse still, nowhere does Ceta contain any workplace protections to stop countries engaging in a race to the bottom. If we do a Ceta-style deal, we’ll constantly be fighting a rearguard action to protect our rights at work.

Instead, Britain’s workers need a deal that not only safeguards the rights we already enjoy, but also in the long run, keeps UK workers’ rights apace with their equivalent in Europe.

The TUC looked at all the available options for a final deal. We think the best option for British workers is for the UK to stay a member of the single market and the customs union. That will protect our rights at work for the long-term – and protect jobs too.

But when the prime minister ruled out staying in the single market and customs union, she emboldened the Brexit extremists, paving the way for the inevitable attacks on workers’ rights that come with a Ceta-style deal.

Brexit promised ordinary working people more control over their lives, not a draining away of power to bad bosses and big corporations. No one voted for that. No one voted to be forced to work excessive hours. No one voted to lose out on their paid holidays or their lunch breaks.

This week, the prime minister can take a stand for working people by standing up to the rogue Brexiteers in her cabinet – and putting all options for a final deal back on the table. Hardworking Brits deserve nothing less.

• Frances O’Grady is general secretary of the TUC