(Adds U.S. State Department comment)

By Anna Koper and Joanna Plucinska

WARSAW, Dec 17 (Reuters) - Poland's parliament passed a media bill on Friday that detractors say aims to silence a news channel critical of the government, in an unexpected move that will stoke concern over media freedom and reopen a diplomatic dispute with the United States.

Critics say the legislation will affect the ability of news channel TVN24, owned by U.S. media company Discovery Inc , to operate because it tightens the rules around foreign ownership of media in Poland.

The vote sours relations with the United States, Poland's most powerful ally, at a time of heightened tension in eastern Europe over an increasingly assertive Russia.

Lawmakers had not been scheduled to vote on the bill, but after a committee convened at short notice to discuss the issue it ended up on the agenda and was voted through in a matter of minutes.

The passing of the bill just before the Christmas break is a success for the ruling nationalist Law and Justice party (PiS), as there had been a question mark over whether it could command enough votes to pass the contested legislation.

The bill must be signed by President Andrzej Duda to become law. Duda, an ally of the government, has previously said https://www.reuters.com/business/media-telecom/polands-president-prefers-media-reforms-market-basis-2021-08-24 that takeovers of foreign-owned media groups should take place on market terms and not with forced solutions, in a sign he could use his power to veto the bill.

"The bill ... will of course be analysed by us and the appropriate decision will be made. I have already talked about the point of view from which I will assess the bill," Duda told reporters on Friday.

The U.S. State Department called on Duda to protect free speech, freedom to engage in economic activity, property rights and equal treatment.

"The United States is deeply troubled by the passage in Poland today of a law that would undermine freedom of expression, weaken media freedom, and erode foreign investors’ confidence in their property rights and the sanctity of contracts in Poland," State Department spokesman Ned Price said in a statement.

The European Commission said the new law sends another negative signal about the respect of rule of law and democratic values in Poland.

"Once this bill becomes a law, the Commission will not hesitate to take action in case of non-compliance with EU law," Commission Vice President Vera Jourova said in a statement.

Opposition lawmakers said the manner in which the committee was convened was illegal and breached democratic standards.

Joanna Scheuring-Wielgus, deputy head of the committee and a member of the opposition Left grouping, said members had been told to attend by text message 24 minutes beforehand, when rules state they should be informed three days in advance.

FOREIGN OWNERSHIP

TVN24's parent, TVN, is owned by Discovery via a firm registered in the Netherlands in order to get around a ban on non-European firms owning more than 49% of Polish media companies. The bill passed by parliament on Friday would prevent this workaround.

The management board of TVN Grupa Discovery called the vote "an unprecedented attack on the free media" and said in a statement the company was "determined to defend their investments in Poland".

Corporate parent Discovery issued a separate statement, saying the parliamentary vote "should alarm any enterprise investing in Poland," and called on Duda to veto the legislation.

The Law and Justice party has long argued that foreign media groups have too much influence in Poland, distorting public debate. PiS says the bill aims to stop countries like Russia or China gaining influence over Polish media.

PiS lawmaker Joanna Lichocka said in a statement, "The rule limiting non-European capital in the media is in line with European law and is valid in many EU countries. This rule has been in force in Poland for years - the amendment seals it up and makes it impossible to circumvent it."

Critics say that moves against foreign media groups seek to limit media freedom and are part of an increasingly authoritarian agenda that has already put Warsaw at loggerheads with Brussels over LGBT rights and over changes to the judiciary that the EU says undermine the independence of courts. (Reporting by Alan Charlish, Anna Koper, Pawel Florkiewicz, Joanna Plucinska, Justyna Pawlak Writing by Alan Charlish Editing by Frances Kerry, Jonathan Oatis and Grant McCool)