The draft document is expected to say Northern Ireland might have to follow EU single market rules in order to avoid a so-called "hard border," should both sides be unable to agree on an alternative solution.
May's coalition ally in Northern Ireland threatened to withdraw support over the issue if a hard border is imposed between the Republic of Ireland and Northern Ireland.
Downing Street has frequently dismissed any potential prospect of a physical infrastructure on the Irish border.
UK anxious about 'unbalanced nature' of the bill
"The U.K. remains concerned about the unbalanced nature of the withdrawal agreement text the EU is set to release," Mujtaba Rahman, managing director at the Eurasia Group, said in a research note.
The legally-binding text comes just days before U.K. Prime Minister Theresa May is scheduled to make her most eagerly anticipated speech on Brexit since last year.
The EU commissioner's 120-page legal text will reportedly refer to three different outcomes for avoiding a hard border between Ireland and Northern Ireland.
Nonetheless, EU negotiator Michel Barnier has said the draft will not contain any surprises because it reflects political pledges made during talks between Britain and the bloc to date.
"Expect the EU to do no more than offer the UK a slightly modified and less attractive version of the kind of deals the EU already has in place with non-EU countries," Kallum Pickering, senior U.K. economist at Berenberg, said in an email.
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