Striking railworkers, post office employees and airline staff are showing "shared contempt" for "ordinary people", Downing Street has said.
In a robust response to a wave of winter strikes, the Prime Minister's spokesman condemned the trade unions accusing them of trying to cause "maximum damage" during the Christmas period.
And Number 10 put the unions on notice, hinting that it could introduce tougher legislation to limit strike powers if the Government felt it was necessary.
It comes as 3,500 post office workers went out on strike for five days in protest over job cuts and pension changes, hitting hundreds of Crown Post Offices.
They join rail workers for Southern Railway, who are staging two days of industrial action on Monday and Tuesday - affecting 300,000 commuters.
The Prime Minister's spokesman said: "There are a number of strikes across different sectors for a number of different reasons.
"If these strikes share one thing in common, it is a shared contempt for ordinary people trying to go about their ordinary lives."
He added: "Their actions are clearly designed to bring maximum damage and disruption during the festive period. But the motivation for the timing of those strikes is an issue for them.
"What our focus has got to be on is the people who are suffering, and how we can encourage all parties to get around the negotiating table and bring these disruptions to an end."
Unite leader Len McCluskey hit back saying: "The Government should be looking at positive ways to resolve disputes, not demonising working men and women who only consider strike action as the very last resort."
Tory MPs have put pressure on Theresa May to introduce legislation to limit the powers of the unions to strike.
But Rob Williams, chair of the National Shop Stewards Network - accused of coordinating industrial action for political ends - said workers would defy tougher rules.
He said unions were acting on issues such as safety, pay and pensions, and told Sky News: "You can bring in all the legislation you like, workers will not accept that."
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Conservative MP for Reigate Crispin Blunt, whose constituents are affected by the rail strike, said it was wrong the railways could hold 300,000 commuters hostage.
Mrs May's spokesman said the Government had already introduced tough legislation on industrial action but would keep it "under review".
British Airways has insisted it will run its full service on Christmas Day and Boxing Day despite the strike.
Post Office director of communications Mark Davies, told Sky News most branches had opened despite the strike and that Royal Mail (LSE: RMG.L - news) 's Christmas postal deliveries would not be affected.
Union officials have denied the strikes have been co-ordinated in an attempt to bring down the Government.
Communication Workers Union General Secretary Dave Ward told Sky News: "Let me make it absolutely clear, we would never sacrifice our members in some higher political objective."
Labour chair of the Commons Public Accounts Committee Meg Hillier warned trade unions "they could be shooting themselves in the foot" with the series of strikes.
"I think if not careful, they could be shooting themselves in the foot."
Virgin Atlantic pilots will also work "strictly to contract" from 23 December and Members of the Transport Salaried Staffs Association and RMT on London Underground are continuing with an overtime ban.