A bid by Roland Koch, leader of the German state of Hesse, to block a contract extension for Nikolaus Brender, editor-in-chief of ZDF, has provoked fury in a country still sensitive about press censorship under the Nazis.
Appealing to the "reason and professionalism" of the ZDF board, which will decide on Friday whether to renew Brender's contract, which expires in March, the letter on Sunday said: "Quality, independent journalism is in everyone's interests."
"This is an overt attempt to oust an independent journalist and strengthen the influence of party politics," the letter added, which appeared in the Frankfurter Allgemeine Sonntagszeitung weekly and magazine Der Spiegel.
And taking a swipe at other, unnamed nations, the letter added: "We can very clearly see examples at the moment in other countries in Europe of what happens when the state does not safeguard freedom."
Brender raised heckles during the recent election campaign in Germany by cancelling a political programme on which Chancellor Angela Merkel and her challenger Frank-Walter Steinmeier had declined to appear.
According to the FAS, Koch, who has a seat on the 16-member ZDF board, has organised a blocking majority to prevent Brender's contract being extended.