Hungary's largest broadsheet newspaper Nepszabadsag has stopped publication, with journalists and the opposition alleging government pressure.
Journalists said it was a "coup" - they were given notice after being stopped from entering the building on Saturday.
The owners said it followed declining sales. The governing party said it was "a rational economic decision".
Nepszabadsag has often criticised Prime Minister Viktor Orban. It opposed last weekend's referendum on refugees.
Mr Orban's government has often been accused of using public media as a government mouthpiece.
A number of private media outlets have also been bought by his allies, critics say.
What other papers say, by BBC Monitoring
The government-backed paper Magyar Idok echoes the government line that the closure was purely the result of economic factors, and that it would be "an infringement of the freedom of the press, if we were to have a say in the decisions of a media owner".
The pro-government news website Origo emphasises that the paper's closure was inevitable, given its plummeting circulation figures and serious financial losses.
However, the left-wing daily Nepszava says that, despite the government's claim that the decision to suspend Nepszabadsag was taken on purely economic grounds, many people will conclude that "today's move is a serious attack on press freedom and democracy".
A commentary by investigative journalist Pal Daniel Renyi on the independent news website 444.hu concludes: "No-one should be in any doubt that Nepszabadsag is the victim of a political manoeuvre."
Nepszabadsag is a leading centre-left daily. It is independent, but tends to support the left-leaning political opposition.
Nepszabadsag's shutdown includes its print and online versions.
A message posted on the paper's Facebook page described the move as a "coup".
"We are in shock. Of course they will try and paint this as a business decision but it's not the truth," a journalist who did not wish to be named told AFP news agency.
Many said the suspension came days after the paper had broken stories of alleged corruption involving senior officials.
Opposition parties said the move showed Mr Orban wanted to suppress press freedoms in Hungary and to gain full control of the media.
The Socialist Party said it was a "black day for the press" and called a demonstration outside the paper's offices at 16:00 GMT.
Mediaworks, which bought Nepszabadsag in 2014, said that its circulation had tumbled by 74% in the last 10 years.