Hundreds of outraged Chinese factory workers held their managers hostage for a day and a half in protest over strictly timed bathroom breaks and fines for being late.

Ten Japanese nationals and eight Chinese managers at the Shanghai Shinmei Electric Co. were held hostage inside the plant from the morning of Jan 18. until 11:50 pm the next day, parent company Shinmei Electric Co. said in a statement on Tuesday.

Shinmei Electric did not officially mention what the workers were protesting, but said management reforms and labor policies may have been the cause.

“The workers demanded the scrapping of the ridiculously strict requirements stipulating that workers only have two minutes to go to the toilet and workers will be fined 50 yuan ($8) if they are late once and fired if they are late twice,” a security guard told AP.

The managers agreed to reconsider the strict rules and were released unharmed after 300 police officers broke up the strike of about 1,000 workers in the factory.

Labor protests have become common in China as factories race to get more productivity from their labor force in a highly competitive market amid workers’ increasing awareness of their rights.