Three low paid workers and their union are launching a legal challenge to make the prime minister seek an extension to the Brexit deadline.
The government has promised EU-law derived employment rights will remain in UK law after Brexit.
But if there were a no-deal Brexit, the union says, ministers would have free rein to water down these rights.
And workers could no longer rely on the supremacy of EU law, the EU Charter of Fundamental Rights or Court of Justice.
The Independent Workers Union of Great Britain (IWGB), which represents some 5,000 workers, 1,000 of whom are EU citizens, is currently relying upon these aspects of EU law in a number of worker’s rights court cases.
Key workers’ rights based on EU law include:
- minimum paid holiday
- working hours regulation
- equal pay
- protection against discrimination
- consultation on redundancy plans
There are an estimated 3.5 million citizens of other EU member states living and working in the UK.
One of them, Maritza Castillo Calle, who has a Spanish passport and works in catering and part-time for the IWGB, is a claimant in the case.
She told BBC News: “Many low paid and precarious workers like me use laws from the EU in order to defend ourselves, and also when a company transfers to another company, to defend our rest, our hours and our rights overall.”
IWGB general secretary Jason Moyer-Lee told BBC News: “Low paid workers, like couriers and cleaners, need all the protections and employment rights they can get.
“Many of these come from EU law and are at serious risk in a no-deal Brexit.
“The IWGB will do everything possible to protect these rights, including legal action to force the prime minister to obey the law and request an extension to the Brexit deadline.”
The IWGB court action is one of three similar challenges being heard this week, which seek to hold the prime minister to the so-called Benn Act.
The act, named after Labour’s Hilary Benn who spearheaded the law’s passage through Parliament, requires the prime minister to write to the EU to request an extension to the 31 October Brexit deadline if a deal has not been signed off by Parliament by 19 October and if MPs have not voted to leave without a deal.
In England and Wales, civil rights group Liberty is bringing a challenge in the High Court seeking assurances that the government will abide by the act.
In Scotland, a separate challenge has been brought to the Inner House of the Court of Session – Scotland’s highest court – by businessman Dale Vince, Jolyon Maugham QC and SNP MP Joanna Cherry.
It will ask judges to consider whether a court can sign a Brexit extension request letter on behalf of the government.
The court will also hear an appeal against a ruling, given on Monday, that Mr Johnson can be trusted to apply the law.
All three actions claim Mr Johnson has repeatedly said he will not seek a time extension in the event of no-deal.
It is argued those statements by the prime minister and members of the cabinet seek to frustrate an act of Parliament and so represent a clear breach of the rule of law.
All three actions seek orders compelling Mr Johnson to comply with the act and send a letter to the president of the European Council seeking an extension to 31 January 2020.
Mr Johnson has previously said the government “will obey the law – and will come out on 31 October” in any event, without specifying how he would achieve these apparently contradictory goals.
The IWGB says such statements are an attempt to frustrate the purpose of the Benn act and are therefore unlawful.
The prime minister’s statements have led to speculation the government has identified a legal loophole to get around the Benn act
If the UK appears to be heading towards a no-deal Brexit on 31 October and the prime minister found a way to get around the Benn act, all three legal challenges could end up at the UK Supreme Court in a dramatic last-minute legal bid to prevent a no-deal departure just days before the deadline.
On Friday, government papers submitted in the Scottish case stated the prime minister would send a letter to the EU asking for a Brexit delay if no deal was agreed by 19 October.
Similar assurances, to obey the Benn act and not seek to frustrate it, have been given by the government to the IWGB in pre-action correspondence seen by BBC News.
However, a senior Downing Street source has said: “The government will comply with the Benn act, which only imposes a very specific narrow duty concerning Parliament’s letter requesting a delay, drafted by an unknown subset of MPs and pro-EU campaigners, and which can be interpreted in different ways.
“But the government is not prevented by the act from doing other things that cause no delay, including other communications, private and public.
“People will have to wait to see how this is reconciled.
“The government is making its true position on delay known privately in Europe and this will become public soon.”
This has led to increased speculation Downing Street has seen a way around the Benn act.