Prime Minister Boris Johnson has won the first of several votes on his plan to undercut the Brexit treaty but faces a growing rebellion among MPs who say breaking international law would tarnish Britain's reputation.
Mr Johnson, who has a majority of 80 in the House of Commons, won the so-called second reading vote on the Internal Market Bill on Monday, 340 to 263.
A wrecking amendment was defeated shortly beforehand, though more will follow.
The EU says Mr Johnson's bill would collapse trade talks and propel the United Kingdom towards a messy Brexit while former British leaders warn breaking the law is a step too far.
A pro European protester stands near Parliament in London. Source: AP
Mr Johnson, though, said it was essential to counter "absurd" threats from Brussels including that London put up trade barriers with Northern Ireland and impose a food blockade - steps he said threatened the United Kingdom's unity.
"The EU still have not taken this revolver off the table," he told parliament before the vote.
"What we cannot do now is tolerate a situation where our EU counterparts seriously believe they have the power to break up our country."
The EU has demanded Britain scrap the main parts of the bill by the end of September and that if not, there will be no trade deal at the end of the year to cover everything from car parts to food.
To back up its message, the European Commission has reportedly delayed a crucial decision on allowing London to continue clearing euro transactions for EU-based clients.
