Polish MPs have passed a controversial new media ownership law that could lead to the country’s largest remaining independent TV station losing its licence, but at the cost of several key votes that put the government’s longterm future in doubt.

After a night of protests in Warsaw and 80 other towns and cities against the bill, which opponents see as an attempt to silence an often critical broadcaster, the law passed on Wednesday by 228 votes to 216 in the 460-seat lower house.

The vote came amid stormy scenes after the prime minister, Mateusz Morawiecki, on Tuesday fired his deputy, Jarosław Gowin, the leader of the junior coalition member Accord, prompting the party to leave the government.

The law – which is expected to be defeated in the senate before returning to the lower house, where an absolute majority will be needed to secure its passage – would prevent non-EU companies from holding a controlling stake in Polish media.

That would force the US media group Discovery to sell its majority stake in TVN, one of Poland’s biggest private TV networks, whose news channel, TVN24, is often highly critical of the Law and Justice party (PiS) that has governed Poland since 2015.

Discovery said in a statement after the vote it was “extremely concerned” but remained “resolute”. It said the bill was “an attack on core democratic principles of freedom of speech [and] the independence of the media”.

The channel appealed to the senate and the Polish president, Andrzej Duda, to oppose the bill and prevent it from becoming law. “Poland’s future as a democratic country in the international arena and its credibility in the eyes of investors depend on this,” it said.

The 13 MPs who formally belong to the Accord group have been increasingly at odds with the main partner in the United Right coalition, the populist PiS, and their departure deprived the government of its one-vote majority.

Gowin said his party was leaving the government “with our heads held high” after expressing deep disagreements over planned tax changes – the so-called Polish deal, intended to win the government re-election in 2023 – and the media bill.

However, PiS successfully persuaded enough MPs from smaller parties to vote in favour of the bill, which has drawn fierce criticism from both the EU and Washington, with Polish media reporting cash and other inducements were on offer.

Earlier the government lost four key votes, including one to suspend the session and postpone a vote on the media law. To howls of “Fraudsters”, the speaker, Elzbieta Witek, a PiS member, ordered another vote, which the government won.

The lost votes do not mean that the end of the government, which would require a formal vote of no confidence, but commentators agree PiS has been weakened and may now need to rely on a critical far-right party, Confederation, for informal support.

The government denies the measure is aimed at any one broadcaster, saying it seeks to prevent potential media acquisitions by non-EU countries such as Russia and China, and has rejected proposals to restrict the ownership ban to non-OECD countries.

But the move follows a sustained government drive to control Poland’s media in which public service outlets such as the state-run TVP television station become propaganda organs for the ruling party, while private, independent media have been steadily driven out of business.

The opposition Civic Platform, led since July by the former Polish prime minister and European Council president Donald Tusk, is determined to defeat PiS and has seized on media freedom as an issue that could unite a broad opposition alliance.

Radosław Sikorski, Tusk’s former foreign minister and a Civic Platform MEP, tweeted on Wednesday: “Our parliament will today be voting to disenfranchise TVN, Poland’s largest, American-owned independent TV station. If the bill passes, we will likely cross the point of no return toward a kleptocratic autocracy.”

Tusk tweeted after the vote: “The parliamentary majority, glued together with the mud of corruption and blackmail, is crumbling before our eyes. It may go on for a while but it is no longer able to govern.”

Washington has urged Warsaw to rethink, saying the proposed law would inevitably harm “defence, business and trade relations” between Poland and the US. Hundreds of Polish journalists and editors have also signed an open letter calling on the government to halt “the destruction of media freedom in our country”.