The nationalist U-turn will allow the Conservative administration to scrap the current six-hour limit on Sunday trading.
Campaigners battling to keep Sundays sacred have described the move as “shoddy” and accused MPs of breaking a “vow” to stand up for shopworkers.
A spokesman for the Christian Institute said: “It seems remarkable that the SNP are on the verge of such a spectacular U-turn in a few short months having initially been so outspoken in publicly condemning the proposals and vowed to stand up for workers’ rights.
“Right-minded people might wonder if some sort of shoddy deal has been cobbled together in the corridors of power with the SNP sacrificing workers’ rights in their pursuit of other agendas.”
The proposals to let councils set Sunday trading laws seemed to be on hold after the SNP said they would oppose them late last year.
With around 20 Tory rebels opposed to the policy, the Government did not have the numbers to pass it.
SNP Westminster leader Angus Robertson claimed that although the legislation would not apply in Scotland it would have an impact since big shops would cut staff wages across the country to make up for the cost of staying open longer.
But when the legislation was discussed by MPs last week the SNP business spokeswoman Hannah Bardell signalled a change. She said: “The SNP have never been opposed to the principle of Sunday trading.
“However, our initial concern and opposition was primarily around the potential knock on impact to Scottish workers. The SNP welcome the provision for additional employee protections that the UK Government has brought forward.”
It’s understood the Government will write safeguards into the legislation ensuring no one is forced to work on a Sunday.
An SNP source told The Sunday Post: “We believe the Government is coming to a position we can support.”
MPs are due to vote on the Enterprise Bill next week.
The trade union that represents shop workers described the Government plans as a “nightmare” and urged MPs to reject them.
Usdaw General Secretary John Hannett said: “Devolution of Sunday trading is the nightmare option that will strangle business in red tape, burden local councils, confuse customers about when shops are open and reduce valuable time shopworkers have with their families as shops open longer on Sundays.”
He added: “The SNP took a strong position on protecting Scottish shopworkers’ pay and that threat looms as large today as it did before Christmas. We now expect the SNP MPs to maintain their opposition to Sunday trading clauses in the Enterprise Bill and not side with a Conservative Government determined to damage the livelihoods of shopworkers across the UK.”