More and more employers are breaking rules meant to protect people in the UK from having to work long hours, trades unions warn.
The Trades Union Congress (TUC) issued a survey on Sunday, the day before its annual conference starts, which it said showed most workers are going way beyond the 48-hour week that European law demands.
Of the 2,000 people it talked to, the TUC said one in four had had to sign a waiver exempting them from the European rule - and had not been given any choice by their employer.
Two out of three, it said, were having to breach the maximum without even being asked to sign the waiver.
That, the TUC warned, was against the law.
"We are declaring war on Britain's long-hours culture," said TUC General Secretary Brendan Barber, announcing a telephone hotline and website that workers could contact to report instances of over-long hours.
"We work the longest hours in Europe, yet other countries are more productive and earn more."
No other European Union country allows opt-outs, Mr Barber said, accusing employers of ignoring the law and relying on the fact that too few people knew their rights.
The long-hours culture, he said, are "a symptom of something sick about our workplaces.
"Long hours are a symptom of badly organised, unproductive workplaces and are too often an easy way out for incompetent managers."
Employers' organisations, though, insist that the opt-outs are necessary to retain business flexibility, and are lobbying hard to retain them when the question is reviewed at the end of this year.