Number 10 has accused a union boss of being unpatriotic for saying that the London 2012 Olympics provides an opportunity for strikes.

A spokesman for the prime minister, David Cameron, warned that a strike during London 2012 would be "completely unacceptable".

In an interview with the Guardian, Len McCluskey, leader of the Unite union, which is Britain's largest, said: "[If the] Olympics provide us with an opportunity, then that's exactly one we should be looking at".

Unions are battling with the government over swingeing public sector cuts, which has seen job losses, pay freezes, and worsening pension deals.

Nick Clegg, the Liberal Democrat deputy prime minister, took a swipe at Labour leader Ed Miliband over his party's financial ties with the unions.

"People will be gobsmacked, appalled, that at a time when we are finally hosting one of the greatest events in the world, [McCluskey] is calling for civil disobedience," Clegg said.

"I know he is the sort of paymaster of the Labour Party but I hope Ed Miliband will rein him in."

Baroness Warsi, a peer and the Conservative Party's chairwoman, also called for Miliband to put his foot down.

"I am shocked that Unite would sink so low as to spoil this great national event for everyone else. Ed Miliband must urgently order his union cronies to rule out disrupting the Olympics," she said.

Labour's shadow Olympics minister Tessa Jowell condemned McCluskey's words.

"No one in our country looking forward to the Olympics, no athlete preparing, and none of our thousands of potential visitors, would understand or sympathise with any disruption to the Olympic Games," she said.

"If this is a negotiation it should take place in private. Unions and employers should get together and sort it out without threats or disruption to Britain's Olympics."