The Unite union is understood to be pushing for Scottish Labour 's Ian Murray to be de-selected in the next general election.
Murray represents Edinburgh South and has been a critic of Jeremy Corbyn.
The BBC are reporting that Unite are pushing for his deselection. Murray was Scotland's only Labour MP between 2015 and 2017.
A contest to replace a sitting MP is triggered if a third of local members or affiliated unions back it.
A vote on the issue is understood to be taking place on Thursday evening.
Murray told the BBC: "It is disappointing that in the week where I'm leading the People's Vote campaign in Scotland...that this is Unite's priority," he said.
"My constituents are my priority and I won't be distracted from fighting for them."
