Poland's fragile governing coalition has been thrown into chaos after prime minister Mateusz Morawiecki sacked his deputy amid a row over media laws.
Mr Morawiecki, leader of the ruling rightwing Law and Justice Party (PiS), ousted Agreement Party leader and former deputy PM Jaroslaw on Tuesday.
The move came ahead of a key vote on a draft media bill. Mr Gowin said his dismissal signalled "the de facto end of United Right".
His party voted on Wednesday to leave the coalition government, meaning PiS has lost its slim majority.
A vote on the bill at the centre of the row, which would prevent non-European owners from having controlling stakes in Polish media companies, was also expected on Wednesday.
Critics said the legislation was an effort to silence an independent, US-owned television broadcaster that is critical of the government.
It would push American company Discovery Inc to sell its controlling stake in TVN, a network with many channels that operates Poland's all-news station TVN24 and has a flagship evening news program watched daily by millions.
The government said the legislation is needed to stop hostile powers from taking over Polish TV networks.
Law and Justice appeared poised to pick up some votes from opposition lawmakers, including some from Confederation, a small party made up of libertarian and nationalist politicians.
A spokesperson for the party said it still expects the law to be passed.
Additional reporting by Associated Press
