Almost one in five new fathers have missed out on paternity pay, mainly because they are self-employed, according to a new study.
Around 130,000 men did not qualify for two weeks' statutory paternity pay, with around 100,000 working for themselves, said the TUC.
Research found that around 30,000 had not been working for their company long enough.
The TUC voiced concern that more fathers do not take paternity leave because they cannot afford to.
General secretary Frances O'Grady said: "All fathers should be able to spend time with their families when a new baby comes along.
"Paid paternity leave and shared parental leave have been important steps forward, but many families are missing out on these benefits - or simply can't afford to use them.
"When fathers share caring responsibilities it helps strengthen relationships, improve child well-being and makes it easier for mothers to continue their careers. We'd like to see all dads being given a right to longer, better-paid leave when a child is born."