David Cameron insisted today that Labour should start "turning back" donations from the Unite union after its general secretary called for civil disobedience during the London Olympics.
Labour leader Ed Miliband described Len McCluskey's comments, also threatening strike action during the Games, as "totally unacceptable and wrong".
But the Prime Minister said Mr Miliband's intervention, in a message on Twitter, was not enough given Unite's financial support for the Labour Party.
"Unite is the single biggest donor to the party opposite, providing around a third of their money, and had more role than anybody else in putting the Right Honourable Gentleman (Mr Miliband) in his place," Mr Cameron said during Prime Minister's Questions in the House of Commons.
"It's not good enough for them just to put out a Tweet, they need to condemn this utterly and start turning back the money."
He said Tory MP Richard Graham, who said Mr McCluskey's remarks would "damage the reputation" of the UK, represented the views of "the whole country".
Mayor of London Boris Johnson urged Mr McCluskey to put political differences to one side for the Olympics.
In a letter to the Unite leader, Mr Johnson said: "All political parties are united in wishing to see the Games as a success and highlighting the very best the UK can offer and I am surprised and disappointed that you believe this is an 'opportunity' for trades unions leaders to cause disruption."
He went on: "I really cannot believe that your members agree with you, and I cannot believe they will support your call for what appears to be an entirely politically motivated attack on the Olympic and Paralympic Games.
"It may be that you have been misquoted in The Guardian, in which case I would urge you to clarify your remarks as soon as possible.
"Whatever our political differences, I believe we should work together to deliver a Games of which London and the UK can be proud."
Mr Johnson also urged Mr Miliband to "disassociate" himself from Mr McCluskey's comments.
"Long after specific disputes and wranglings are forgotten, the Olympic and Paralympic Games will be in the UK's collective memory. I am sure we all agree we want that memory to be one of which we can all be proud," he said in a letter to the Labour leader.
"Therefore I am calling on you, as the Leader of Opposition, with strong and honourable links with the trades union movement, to disassociate yourself fully from such comments and persuade others to do likewise."
Mr Miliband said later it was "totally wrong" to make threats against the Olympics and said he condemned Mr McCluskey's comments.
"It's completely wrong to make any threat to the Olympic Games. I do condemn it. We as a Labour government fought for the Olympic Games to be brought to Britain as part of the cross-party effort," he said.
"It is a moment of national celebration, it is a moment when the focus of the world will be on Britain and I think it is totally wrong to make threats to the Games."