Polish lawmakers passed a new child benefit scheme Thursday which will give monthly payments of 500 zlotys ($125) for all second and subsequent children in a family.

The passage of the law in the lower house of parliament fulfills one of the key campaign promises of the populist, conservative Law and Justice party, which won power last year vowing to help families and encourage more births in a country with one of the world's lowest birthrates.

"This is a very important day for Polish families," Prime Minister Beata Szydlo told lawmakers before the vote. "This is the day when we can finally say that Poland has joined those states that know that a wise pro-family policy is a matter of the national interest."

The government will begin paying the benefits in April for all second and subsequent children up to the age of 18. Extremely poor families will be able to receive the payments also for a first child.

Political opponents say it discriminates against an estimated 3 million children, including those in one-child families; that it won't stop the country's demographic decline; and that paying for it will hurt state finances.

The child benefits are one element of a larger program to increase social spending, something that Law and Justice sees as a corrective to years of pro-market policies which enriched some Poles but left many people struggling on very low wages.

To pay for increased social spending, Szydlo's government has raised taxes on banks and plans to do the same for large retailers.

On Thursday, about 5,000 Polish shop owners held a protest in front of parliament against the plan to raise the tax on retailers. The government had intended for the tax to hit foreign supermarkets, but Polish entrepreneurs say they fear they will be hurt too.