More than four out of ten UK workers are "in the dark" as to their holiday and paternity leave entitlements, the TUC has said.
One in seven people believed they had no rights to leave, the survey found.
In addition, one in five workers thought they could be forced to work more than 48 hours a week, a practice forbidden under EU law.
The TUC said the findings were "alarming " and showed bad bosses were failing staff.
"While good employers make sure they comply with new laws, there are bad bosses out there who try to duck their responsibilities whenever they can," said Brendan Barber, TUC general secretary.