Statutory maternity pay for UK mothers is among the worst in Europe, according to an analysis by the TUC.
The trade union body says only Ireland and Slovakia have worse "decently paid" entitlements.
It defines decently paid as two-thirds of a woman's salary or more than £840 a month.
The government said the UK's maternity system was one of the most generous in the world and most mothers could take up to 39 weeks of guaranteed pay.
That was nearly three times the EU minimum requirement of 14 weeks, a statement said.
The TUC argues that statutory maternity pay should be at least as much as the minimum wage so mothers do not have to return to work prematurely.
"The UK is in the relegation zone when it comes to decently paid maternity leave," said Frances O'Grady, general secretary of the TUC.
"Many European countries offer decent support to new mums, but lots of parents here are forced back to work early to pay the bills."
The analysis is based on research by the Leave Network, an international group that analyses and researches leave policies.
What are your rights?
- Most employed mothers are entitled to 52 weeks' maternity leave
- Statutory maternity pay for eligible women is usually paid at 90% of their weekly wage for the first six weeks, with the remaining 33 weeks at £139.58 a week or 90% of their weekly wage, whichever is lower
- Women who earn less than £112 a week are not eligible for statutory maternity pay; instead most can claim maternity allowance.
While some companies have more generous schemes, Ros Bragg, from the campaign group Maternity Action, said the "vast majority" of women in the UK received statutory maternity pay. Employers then claim this back from the government.
"The UK stands out as having a relatively long period of maternity leave but a relatively low amount of pay... it drops off very quickly," she said.
"And the beginning of the maternity leave is exactly when it is most useful."
The TUC also thinks shared parental leave should be more flexible - so parents can take their leave in smaller chunks, rather than all at once.
European league table of 'decently paid' maternity leave
- UK comes 22nd out of 24
- Croatia comes top, with six months
- Poland, Hungary, Czech Republic are next, with more than four months
- Estonia, Italy, Spain, Belgium, Denmark, France, Malta, and Switzerland offer more than three months