WARSAW — Polish teachers' unions on Friday rejected a pay offer from the government and vowed to walk off the job on Monday — causing a massive political headache for the ruling Law and Justice (PiS) party.

The government pay proposal "only worsens the conflict," Sławomir Broniarz, the head of the Polish Teachers' Union, told reporters after talks broke off on Friday morning, adding it "leaves no possibility of coming to an agreement."

If the walkout goes ahead, it will disrupt school exams and could even affect the outcome of the European Parliament election — where PiS is neck-and-neck with the opposition European Coalition.

The problem for the government is that in anticipation of the election it announced a very generous package of welfare policies, covering everyone from children to pensioners. The promises would cost about 40 billion złoty (€9.3 billion), or about 2 percent of GDP. The finance minister was dismayed at the unexpected promises, and the government is scrambling to find the needed money in order not to overshoot EU fiscal rules.

The new social policies will increase Poland’s deficit, which was just 0.5 percent of GDP in 2018. Credit rating agency Fitch warned last week that it could rise to 2.8 percent in 2020 — brushing against the EU’s 3 percent deficit limit.

"We are filing a motion of no-confidence in the minister of education" — Sławomir Neumann, head of the largest opposition party

"The budget deficit is an important question. We are firmly keeping to the Union framework and we want to stay there," Prime Minister Mateusz Morawiecki said last week. However, he added: "The budget is not bottomless, it's not made of rubber."

That annoyed the country's half a million teachers, who aren't seen as being natural PiS supporters. They feel they've been left out of generous benefit schemes aimed at larger families and the elderly — key ruling party constituencies.

Relations with the government were already tense after its 2017 overhaul of the education system. Defying opposition from parents and teachers’ unions, the government abolished middle schools, returning to the communist-era system of just primary and secondary schools.

Teachers have also griped about their low pay; the median monthly salary of a teacher is 3,983 złoty (about €929) a month — less than the average monthly national salary.

The Polish Teachers' Union initially wanted an across-the-board pay rise of 1,000 złoty a month, and is now asking for a pay hike of 30 percent.

The union estimates that a 1,000 złoty raise would cost about 10 billion złoty, but the government doesn't have much left in the kitty to spend on teachers.

Instead, the government proposed extending mandatory teaching hours, and a raise of 9.6 percent.

"There are no indications that would allow us to discuss stopping the strike on Monday," Broniarz told reporters after receiving the offer.

The government and its media supporters have attacked the unions. Adam Bielan, the deputy speaker of the Senate and who is close to PiS leader Jarosław Kaczyński, said that the strike is being organized by an “extremely politicized organization.” However, Poles are broadly sympathetic, with 47 percent saying they support teachers striking for higher salaries, while 36 percent are opposed, according to a poll this week.

For PiS, the timing is terrible. The strike risks disrupting exams, which begin in middle schools on April 10. School-leaving exams start on May 6, less than three weeks before the European election.

The opposition has seized on the issue and is attacking Education Minister Anna Zalewska, who devised the controversial education reforms. She is a candidate for the European Parliament, and is expected to win a seat.

"We are filing a motion of no-confidence in the minister of education," tweeted Sławomir Neumann, head of the parliamentary caucus of Civic Platform, the largest opposition party.

Civic Platform is also promising to increase teacher salaries by 1,000 złoty a month if it takes power in this fall's national parliamentary election.

Talks between the government and the unions are due to resume on Sunday. If they don't succeed and teachers walk out on Monday, PiS will face the outrage of a very large constituency of voters: parents.