WARSAW, Poland (AP) — The union leader of Poland’s striking teachers says that key high-school graduation exams next month could be cancelled if government does not respond to pay demands.

Slawomir Broniarz warned that the exams, scheduled for May, may not happen because the strike may prevent the qualification procedure.

On Friday, teachers were on strike for the fifth day in a row as part of an indefinite action related to their 30% pay demand. The government is urging the strikers to accept an offer of half that amount.

Rallies were held in Warsaw and many other cities across Poland in support of the teachers’ pay demands.

Friday was the last day of middle school exams, which were held in spite of the strike action. On Monday, primary school exams begin.

Teachers’ monthly earnings range from 1,800 zlotys to 3,000 zlotys ($470 to $780).