Ed Miliband has sanctioned a public slapdown of the leader of Labour's biggest trade union donor over a "reprehensible" attempt to divide the party.
Unite general secretary Len McCluskey launched an outspoken attack earlier on a number of shadow cabinet figures, warning the Labour leader he would be "cast into the dustbin of history" if he was "seduced" by Blairite members of his team.
Mr Miliband was elected to Labour's top job on the back of union votes and receives millions in funding from Unite.
A spokesman for Mr Miliband said: "Len McCluskey does not speak for the Labour Party. This attempt to divide the Labour Party is reprehensible. It is the kind of politics that lost Labour many elections in the 1980s. It won't work. It is wrong. It is disloyal to the party he claims to represent."
The strongly worded statement was issued after Mr McCluskey appeared to indicate he wanted a number of shadow cabinet ministers sacked.
In an interview with the New Statesman magazine, the union leader picked out shadow foreign secretary Douglas Alexander, shadow defence secretary Jim Murphy and the shadow work and pensions secretary Liam Byrne for particular criticism.
He warned the Opposition leader that listening to the men would lead to defeat and urged him to go into the election with "a team that he's confident in".
"Ed Miliband must spend most of his waking hours grappling with what lies before him," Mr McCluskey told the New Statesman.
"If he is brave enough to go for something radical, he'll be the next prime minister. If he gets seduced by the Jim Murphys and the Douglas Alexanders, then the truth is that he'll be defeated and he'll be cast into the dustbin of history."
He added: "Liam Byrne certainly doesn't reflect the views of my members and of our union's policy, I think some of the terminology that he uses is regrettable and I think it will damage Labour. Ed's got to figure out what his team will be."