U.K. Prime Minister Boris Johnson’s plan to renege on part of the Brexit divorce deal passed its first hurdle in Parliament late Monday after a bruising debate in which senior members of his own party denounced the move.

The House of Commons passed the Internal Market Bill by 340 to 263 in its first main vote, allowing it to go through to the next stage in the parliamentary process on Tuesday.

The prime minister said the proposed legislation, which will rewrite part of the Withdrawal Agreement, is "essential” to maintain the U.K.’s economic and political integrity. He accused the European Union of making "absurd” threats to stop food moving from mainland Great Britain to Northern Ireland.