In a letter to the Herald newspaper Cummings said: "It is surprising and disappointing that the SNP, which is happy to allow shops and garden centres here in Scotland to open for a full day on a Sunday, has announced it will seek to block the UK Government’s plans to give the powers to local authorities in England and Wales to enable the same opening hours there.
"Whatever the merits of the political tactics employed on behalf of the SNP in Westminster, the claim that Scottish workers will have their pay cut as a result is without foundation. Premium wages for working on a Sunday is an exception and not the rule in Scotland, and Scottish workers will continue to receive the same pay regardless of any locally introduced changes to Sunday working patterns in England and Wales.
"In fact the SNP position will deny economic growth opportunities for Scottish-based businesses with outlets in England and Wales. Surely the SNP appreciates the value of devolving powers from Whitehall so that local communities can decide what is most appropriate for them?
"For many families and hobby gardeners an outing to a garden centre to enjoy the plants, gardens and hospitality is a favourite way to spend time on a Sunday together. Quite apart from the benefits to garden centre businesses of extended Sunday opening it would serve to extend the opportunity for family, leisure and community time already enjoyed by families here in Scotland."
HTA horticulture head Raoul Curtis Machin said: "We are disappointed that the SNP MPs are choosing to make this a political football, when the evidence for their claims seems flimsy at best. We hope to meet with some of them to discuss in more detail and explain the potential constraints they will put on our sector for growth."