The Government could bring in fresh anti-strike legislation if unions continue to threaten action to coincide with the Olympics or the Royal Wedding.
David Cameron said he was "happy to look" at new laws that would prevent strikes unless more than half of the members who were balloted voted in favour.
The proposal is designed to stop strike action with low turnouts. Mr Cameron also co-authored an article with Boris Johnson, the London Mayor, in The Sun, accusing unions of "cynical timing" by threatening strikes during big national events. "The Royal Wedding and the Olympics present amazing opportunities for our country to show the world the best of British," they wrote.
Len McCluskey, general secretary-designate of the Unite union, said: "We have in place legislation from the 1980s that already makes it very difficult to call a strike – and even when the ballot is conducted to the highest standards the courts often intervene on a technicality."