LONDON (BLOOMBERG) - Prime Minister Theresa May came under fresh pressure from those in her Conservative Party who want a swift, clear break from the European Union, as 62 lawmakers set out their Brexit demands in a letter.

The group of lawmakers appeared to challenge the government's plan for the transition deal that businesses want, and said Britain must not be forced to follow EU regulations after it leaves.

Britain must be able to sign trade deals immediately after the split, according to the lawmakers.

"The UK must be free to start its own trade negotiations immediately," the letter, organised by the European Research Group, a caucus of Tories wanting a maximum distance from the EU, said.

"Your government must have the ability to change British laws and rules once we leave, rather than being a 'rule-taker."'

The letter, sent to May on Feb 16, was released to the press on Tuesday, after May and her Brexit Secretary David Davis made speeches suggesting Britain would stay in very close regulatory alignment with the EU after it leaves.

It is the closest the ERG has come to releasing its membership list, and suggests that at least a fifth of Conservative lawmakers want a hard break from the bloc.

May doesn't have a majority in Parliament and depends on 10 lawmakers of the Northern Irish Democratic Unionist Party to govern.

The ERG said they supported May's leadership, even as they set out their demands.

While the letter stopped short of telling May to drop her transition plan altogether, what it called for is quite different from the "no change" period that May and her ministers have told businesses they can expect next year.