The leading frontbencher, tipped as a future Labour leader, said attempts to purge moderate Labour politicians by Momentum was “heartbreaking” and not the way forward for the party.
Momentum, set up to shore up support for Jeremy Corbyn following his shock rise to the leadership, is ordering Labour parliamentary candidates to swear allegiance to the leader if they want their support.
Ms Rayner told The Times: “I’m not Momentum. I’m not Progress. I’m not trade union. I’m a Labour MP to represent all of my constituents.
“Any factionalism in the Labour Party will damage us and remove us from getting near power, which ultimately damages the people that need our support.”
GETTYAngela Rayner has refused to sign a pledge of allegiance to Corbyn
Im not Momentum. I’m not Progress. I’m not trade union.
The 13-point “political accord for Momentum-backed candidates” asks candidates to “work to ensure the Labour manifesto - subject to future policy development - is fully implemented once Labour are in government.
The signed contract, described by critics as “Stalinist”, says members will commit to “revitalise the Labour party by building on the values, energy and enthusiasm of the Jeremy for Leader campaign”.
Corbyn’s fan club has been accused of trying to purge moderate MPs and councillors, who are insufficiently supporive of Mr Corbyn.
Ms Rayner added: “Trying to deselect and get rid of people’s voices is not a way forward. We have disagreements.
“There’s not been a Labour leader with whom I agree on everything, but Corbyn has an absolute right to lead our party and our MPs have an absolute right to be there and to have their voices heard and so do our councillors.
“Our MPs have an absolute right to be there and to have their voices heard and so do our councillors who do a tremendous job.
“They’ve had seven years of austerity, managing the decline when central Government have cut their money, but they are always thinking about how they can support their communities and do the right thing.”
Momentum is already exerting a tight grip on Labour.
GETTYThere are fears Corbyn's party is being taken over by Momentum
Its numbers have continued to swell since the Labour conference, adding 1,500 new members to its books.
The group now claims to have 31,000 members across the country.
The rise of Momentum has seen long-serving councillors who have spent years doing their public duty are now being forced out of their positions by Labour’s radical left.
Councillors across the country have been deselected in a vote of local members or have faced pressure to announce they do not intend to re-seek election.
In Haringey, north London, 10 Labour councillors have stood down or lost the seat they hoped to contest to a more left-wing candidate.
It comes after party grandee Roy Hattersley warned Labour is facing its greatest ever crisis as the extreme leftwing pressure group Momentum tries to launch a systematic takeover of the party.