ISTANBUL, Turkey (CNN) -- The Organization for Security and Cooperation in Europe on Wednesday added itself to a growing number of European voices expressing alarm at a record fine levied against Turkey's largest media conglomerate.
Recep Tayyip Erdogan earlier this year on the campaign trail.
The Turkish government last week decided to fine Dogan Holding $2.5 billion for alleged unpaid back taxes.
"The amount of penalties levied upon the Dogan Group is unprecedented and alarming," wrote Miklos Haraszti, the OSCE's media freedom representative, in a letter to Turkey's foreign minister Wednesday.
The OSCE is the world's largest security-focused intra-governmental organization, with a mandate that includes conflict prevention, crisis management and post-conflict rehabilitation.
Haraszti wrote that the "unprecedented and alarming" fine posed a threat to media pluralism in Turkey.
The rebuke comes after Turkish Prime Minister Recep Tayyip Erdogan denied accusations that the fine was politically motivated.
"I believe it is not right to mistake the routine works of the state agencies with freedom of press," Erdogan said, according to Turkey's state news agency, Anatolian.
Erdogan spoke Monday at a dinner in the Turkish capital attended by European ambassadors.
"I have no right or authority to exert political or economic pressure on press organs. Neither do they have the right to assume privileges against the law," Anatolian Agency also quoted Erdogan as saying.
Last week, the Turkish finance ministry slapped Dogan Holding with the whopping fine for three years of unpaid taxes.
According to its Web site, Dogan Holding's total assets as of June 30 amounted to the equivalent of approximately $2.8 billion. Dogan's stock prices plummeted last week on news of the penalty, which economic analysts say may be the highest in Turkish history.
Dogan Holding is a sprawling, Istanbul-based company with interests in oil and gas, manufacturing, agriculture and tourism. It also owns an armada of TV channels, newspapers and publishing companies, in addition to CNN Turk, a joint venture owned by Dogan Holding and Turner Broadcasting International.
Turkish academics, political analysts and journalists argue that over the years, the company's chairman, billionaire industrialist Aydin Dogan, profited from cozy relationships with previous Turkish governments.
"There was a system of corrupt relations, basically, very much politicized relations between media and politics," said Yasemin Congar, deputy editor-in-chief of the independent newspaper Taraf, and a former reporter for a Dogan newspaper.
"Many media companies, including Dogan Group, became as big as they are thanks to the politicians in the past basically turning a blind eye to their misdoings, giving them extraordinary opportunities that were not given to other companies," Congar said.
Executives at Dogan Holding reject these accusations.
"Like any group in Turkey, doing business in Turkey means you have to approach the bureaucracy of the government. But we haven't benefited," said Volkan Vural, a top adviser at Dogan Holding.
Last winter, however, a war of words erupted between Dogan and the Turkish prime minister after Dogan's media outlets reported on an alleged corruption scandal involving top officials in Erdogan's party.
While campaigning in municipal elections, Erdogan called on his supporters to boycott Dogan's newspapers. And last February, the Turkish government fined Dogan Holding half a billion dollars for alleged irregularities arising from the sale of shares to Axel Springer, a German publishing company.
"I do think there is a political aspect to it," said Congar. "I think when Mr. Erdogan sees (Dogan Holding), he sees a political enemy, not a media outlet."
Dogan Holding newspapers and TV channels have slammed the tax fine, accusing the government of trying to destroy critics in the media.
"Assault on the Press. Power to tax. Power to destroy," read a headline Tuesday on the Dogan-owned, English-language Hurriyet Daily news Web site.
"It's cold-blooded murder, nothing else," said Mehmet Ali Birand, anchor and editor-in-chief at Kanal D, a Dogan Holding TV station.
The $2.5 billion fine has also raised concerns among media watchdog organizations and the European Union.
"While tax irregularities should indeed be penalized, one can expect the sentence to remain proportional to the alleged offense," European Commission spokesman Amadeu Altafaj Tardio wrote in an e-mail to CNN. "When the sanction is of such magnitude that it threatens the very existence of an entire press group, like in this case, then freedom of the press is at stake."
The media war with Dogan Holding could jeopardize the Turkish government's already troubled bid to become the first predominantly Muslim country to join the European Union. Tardio wrote that "this latest decision" would be taken into account in a progress report on Turkey's membership negotiations, due to be published Oct. 14.
David Dadge, director of the Vienna-based International Press Institute, said the group is concerned that the original tax investigation "was more motivated by political and personal calculations rather than a genuine desire to carry out a full and fair investigation of the Dogan media group's financial circumstances."
In a statement released Monday, the Turkish finance ministry denied singling out Dogan Holding.
"The Dogan Yayin Group has not been the only group under examination by the Income Controllers. A majority of the media sector has been subject to examination," the finance ministry said in its statement.
Dogan has said it will appeal the fine.