Tony Blair risks losing the votes of traditional Labour supporters through his EU summit negotiating stance, a major trade union leader has warned.
The union says the UK must not "cherry pick" European law
Ministers are trying to ensure new EU plans do not affect UK strike laws.
Transport union leader Tony Woodley said UK workers should get protections available elsewhere in Europe.
He said: "What we are seeing here is a government pushing through policies and programmes that clearly don't meet favour with the working men and women."
The criticisms surround the proposed Charter of Fundamental Rights. Downing Street is anxious in case it impinges on UK bans on secondary picketing and laws on strike ballots being held in secret.
Mr Woodley, general secretary of the Transport and General Workers' Union, told BBC Radio 4's Today programme he did not want those two changes.
But he argued there should be no "cherry-picking" of European rules.
He urged the prime minister to take heed of last week's election results - "the worst in living memory of any party in power".
"We want a radical third term for a Labour government but by blocking workers' rights, by blocking protection for the workers in this country, all we are doing is turning traditional Labour voters off," he said.
Mr Woodley went on: "We wish they would try more to get themselves elected rather than unelected."
And he accused business leaders of scaremongering over the proposed charter.
But Digby Jones, director-general of the Confederation of British Industry, said it was the trade unions who were spreading unfounded fears about bad behaviour among employers.
He said Mr Woodley appeared to be "marching valiantly towards 1970".
Highlighting business rivalry from India and China, Mr Jones said: "We have to be able to ensure that the whole of the European Union - this is not a British issue - is competitive in a globalised world."
He said business bosses did not oppose UK workers having the same rights as their European counterparts as long as the EU rules offered the flexibility needed for effective competition.