Government plans to loosen Sunday trading laws in England and Wales are facing defeat in the Commons after the SNP indicated it will oppose them.
The party is ready to join forces with Labour and around 20 Tory rebels to block the changes amid fears they could drive down Scottish workers’ wages.
Chancellor George Osborne outlined proposals in the Budget earlier this year that would devolve powers to set Sunday trading rules to local councils and mayors.
Currently large stores and supermarkets can only open for six hours on Sundays.
The SNP has apparently been convinced by shopworkers’ union Usdaw that retailers would fund extra opening hours by cutting the wages paid on Sundays across the UK.
Angus Robertson, the SNP’s Westminster leader, said: “SNP MPs could hold the balance of power in the House of Commons on Sunday shopping and we will not undermine shop workers.
“This legislation will impact on workers in Scotland and elsewhere in the UK and no pay safeguards have been offered by the Westminster government.
“The SNP will continue to work with the representatives of shop workers and we will oppose the Tory proposals.”