WARSAW (Reuters) - Teachers across Poland held a strike on Monday following failed talks over their demands for higher pay, putting pressure on the government before parliamentary elections later this year.

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More than half of schools were closed in several large cities, where support for the government of the Law and Justice (PiS) party is generally lower. Nearly 80 percent of teachers were on strike in the capital, Warsaw, according to the state news agency PAP.

PiS has seen its popularity erode during a series of scandals, with local media accusing the party of allowing excessive pay at the central bank and running a murky real estate business. PiS denies any wrongdoing.

In recent weeks, some opinion polls conducted before a European Parliament election in May have raised the possibility that PiS might lose power after the general election due in October or November. It is the first such signal since the conservative party came into government in 2015.

In an apparent attempt to shore up its voter base, PiS, which espouses a left-leaning economic agenda, has announced new public spending programs in February. Many public-sector workers also demanded higher pay.

“The sense of surprise among teachers that money was not found to compensate them for their hard work was huge,” a senior trade unionist from the western city of Poznan, Wojciech Misko, told public broadcaster TVN.

Many teachers are also unhappy with what they say has been chaotic education reform.

Talks between three teachers unions and the government ended on Sunday evening, with some sticking by their demand for a monthly salary increase of 1,000 zlotys ($262). Only one, smaller union accepted the government’s offer of a 15 percent monthly increase starting in September.

“My sense from the talks was that the unions were saying: deduct money from the broad social programs and give it to us,” Beata Szydlo, a deputy prime minister, said.

Teachers’ salaries in Poland range from 3,045 to 5,603 zlotys per month. Official data in February showed the average corporate salary in Poland was around 4,949 zlotys.