MPs are set to vote on handing control of the issue to local councils, which would give the option to extend Sunday opening in England and Wales by up to six hours.
The SNP was expected to abstain in the vote, according to reports, because there are no Sunday trading restrictions in Scotland.
But the party has now said it plans to vote against extending hours in England and Wales, which it said could negatively affect shopworkers’ pay in Scotland.
Stewart Hosie, deputy leader of the SNP, said Scottish workers were paid extra for working on Sundays. He noted that there were no guarantees that these higher wages would be protected if hours were extended in other parts of the UK.
When MPs vote on the matter the government could now face defeat if the SNP links up with Labour and a number of Conservative backbenchers who are opposed to the plans.
The SNP announcement will be good news for small stores in England and Wales.
James Lowman, the chief executive of the Association of Convenience Stores said: “Longer opening hours will serve only to benefit out of town stores, whilst hurting high streets, Post Offices and small shops – resulting in a net loss of jobs to the economy.”
Meanwhile, those in favour of the proposal to extend Sunday hours say the move would better help retailers compete with online shopping.
Speaking to BBC Radio 4’s Today programme, conservative MP Grant Shapps said: “It is two decades since these rules were first set. The internet hadn’t even been invented at the time.
“We’ve now got a situation where people can get shopping delivered on a Sunday but you can’t go into a shop and buy. It’s a bit ridiculous and it’s time to update these rules.”
Since 1994, small shops (around 3,000 sq fit in size) in England and Wales can open when they want to every Sunday but stores over this size must trade for just six hours between 10am and 6pm.