Former shadow Scottish Secretary Ian Murray branded the pledge a "little bit ridiculous" and insisted the focus should be on Brexit.
"My loyalty has never been in question to the Labour party," he told BBC Politics Scotland today. “Indeed my pledge is every single weekend when I'm out knocking on doors, delivering leaflets, staffing streets stalls and doing advice sessions with my constituents - that's my pledge to the Labour party.
"I think these pledge things are a little bit ridiculous in my view. I won't be signing it for a number of reasons - first of all because I think it's unnecessary."
The pledge has been seen as means to shore up support for Jeremy Corbyn amid renewed speculation of moderate Labour MPs walking out to form a new centrist party.
But Mr Mr Murray, the Edinburgh South MP, said it is a Labour majority government which is needed for the country.
"It's one of these things that happen and I just don't think we should be signing these pledges. We should be getting on with the task of trying to resolve this issue which is number one on the agenda at the moment."
Mr Murray insisted that he will remain in the Labour party and has no plans to quit.
The party should be focusing on Brexit, he added, and securing a second referendum "with an option to remain."
Mr Corbyn, though, was accused of "doing everything he possibly to put barriers in the way" of holding a second referendum.