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 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 (Miliband) in his place," 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".
Downing Street earlier denounced the threat of strikes to disrupt the Olympics as "completely unacceptable and unpatriotic".
The party leaders also clashed over the government's controversial NHS Bill. Miliband said the government were 'digging their own burial" with the legislation, a warning it would cost them the next election.
"It's hard to keep track of opposition to this Bill," he said. "Every week that goes by more and more health organisations come out against this Bill."
But Cameron said Miliband opposed putting extra money into the health service and accused him of performing a U-turn on whether he supported key measures in the Bill.