Boris Johnson has urged MPs to support a bill which modifies the Brexit deal he signed with the EU in January.
The PM said the Internal Markets Bill would “ensure the integrity of the UK internal market” and hand power to Scotland and Wales.
He also claimed it would protect the Northern Ireland peace process.
Critics say the move will damage the UK’s international standing after a minister admitted the plans break international law.
The Scottish government has not ruled out legal action to prevent it becoming law.
Scotland’s First Minister Nicola Sturgeon said: “The Tories’ proposed Bill for a so-called UK internal market is an abomination. It is a naked power grab which would cripple devolution.”