An investigation has been launched into a parliamentary debate and controversial vote held in an ancillary hall of parliament during an opposition MP sit-in in the main hall.

On Thursday, Warsaw’s District Prosecution launched an investigation into whether there was an “abuse of power, breach of duty and working against the public interest” by public officials.

Opposition parties Civic Platform (PO) and Nowoczesna called for the investigation earlier in the year, claiming the law may have been broken by the Speaker of the lower house Marek Kuchciński and other officials from the governing Law and Justice (PiS) party.

Kuchciński came under fire when he excluded an opposition deputy from debate in parliament on 16 December after the MP raised the issue of contentious plans to change media access to the parliamentary building.

Opposition MPs then stormed the rostrum, blocking proceedings, and conducted a sit-in.

After several hours of recess, the debate was moved to an ancillary hall, and a key budget vote was held by a show a hands.

The vote was slammed as illegal by opposition parties, who questioned whether a quorum was met. Some opposition MPs also claim they were not allowed entry into the ancillary hall and were therefore not allowed to take part in the vote.