Donald Tusk and Jean-Claude Juncker have written a letter to Theresa May claiming they do not want the so-called "backstop" to be permanent post-Brexit.
The letter from the European Council president and European Commission president was published today, and stated the controversial backstop would be a temporary measure.
Many Conservative MPs are threatening to vote down the deal tomorrow because of their concerns that the UK could be permanently trapped in the backstop arrangements - designed to avoid a hard border in Ireland and requiring compliance with some EU rules - and be unable to pull out without approval from Brussels.
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However, in the letter, the EU presidents confirmed that the backstop would "only be in place for as long as strictly necessary".
The European Union "does not wish to see the backstop enter into force", as it would represent a "sub-optimal trading arrangement for both sides", they wrote.
WATCH: Theresa May speaks in Stoke-on-Trent
The letter also stated that the EU were "not in a position" to amend or rewrite the Withdrawal Agreement, which will be voted on by MPs tomorrow.
"It [Withdrawal Agreement] represents a fair compromise and aims to ensure an orderly withdrawal of the United Kingdom from the European Union, thereby limiting the negative consequences of Brexit," they said.
Addressing a crowd in a factory in Leave-voting Stoke-on-Trent, the Prime Minister referenced the letter, saying it made it clear that the backstop was "not a threat or a trap".