WARSAW (Reuters) - Poland's governing nationalists announced legislation on Wednesday to ensure final high school exams are held next month despite a teachers' strike that has shut thousands of schools for more than two weeks.

Teacher demands for a pay rise of up to 1,000 zloty ($260)evoke the competing demands of various groups for a slice of the fast-growing prosperity of central Europe's largest economy, at a time when the ruling Law and Justice party (PiS) is expanding benefits for families and pensioners ahead of elections.

Critics say the government lacks incentive to find extra money for teachers as they broadly oppose the PiS over accusations that it is undermining Polish democracy by seeking to impose more political control over the judiciary, the state media and other public institutions. Meanwhile, the populist PiS has announced more payments for farmers who raise pigs and cows.

Teachers polled by the Rzeczpospolita daily say they earn 1,750-2,800 zloty a month after taxes. The average net salary in Polish enterprises amounts to around 3,700 zloty.

Students and parents are anxious to know whether final high school exams - allowing students to apply to university - will be held as planned at the beginning of May.

"The state must guarantee that in every school every exam candidate will be able to take their exam at the scheduled time, this is necessary for the peace of mind of students and parents and for the state to be seen as serious and responsible," Prime Minister Mateusz Morawiecki said in a televised speech.

He announced pending legislation that would allow school directors to grant permission for exams to go ahead if the teachers' committees at schools remained on strike.

The emergency bill is expected to be put to a vote on Thursday. Given the PiS's majority of 237 seats in the 460-strong lower house of parliament, the announced legislation is likely to be passed.

Despite a majority of Polish schools not holding lessons for a third week, final exams for children finishing primary and middle schools were held without disruptions.

Thousands of teachers took to the streets of Warsaw on Wednesday as the strike stretched into its 17th day, brandishing placards with slogans such as "Without respect and money, education drowns in poverty".

In recent months, some opinion polls conducted before the European Parliament election in May have raised the possibility that PiS might lose power after Poland's national election due in October or November. It is the first such signal since the strongly conservative party took office in 2015.

($1 = 3.8296 zlotys)

(Reporting by Alan Charlish, Anna Wlodarczak-Semczuk and Marcin Goclowski; Editing by Mark Heinrich)