Ukrainian broadcasters have criticised a government order banning national TV and radio programmes in Russian, which is spoken by most Ukrainians.
The head of one TV channel described the move as a ploy ahead of presidential elections this autumn.
Although Ukrainian is the national language, many TV and radio stations currently broadcast in Russian.
The decision obliges broadcasters to change all their programming to Ukrainian or face tough penalties.
The BBC's Helen Fawkes in Kiev says Ukraine has struggled to re-establish Ukrainian as the national language following independence from the Soviet Union more than a decade ago.
While it is spoken by the president in parliament and in large parts of the country, there are areas, mainly on the border with Russia and in the east, where Ukrainian tends not to be used.
Russian is the first language of 22% of the population.
Vote-winner
The national council for TV and radio broadcasting claims that by broadcasting to cater for these people media outlets are turning Ukrainian into a minority language.
The penalties for violating the new rules will include warnings and fines but they could go as far as suspension or even the withdrawal of broadcasting licences.
This will mean that Russian-language films or programmes will need a Ukrainian translation or subtitles.
Our correspondent says that in the run up to the presidential election the ban could be a vote-winner for the current administration in predominantly Ukrainian-speaking areas, particularly in the west of the country which traditionally supports the opposition.
It is also certain to provoke anger in Moscow which is critical of the treatment of Russian-speakers in Ukraine, she says.
Olexander Tkachenko, president of the private Novy Kanal station, said the move was unfair on many broadcasters.
"Ahead of an election, it would have been difficult to come up with something better as a pretext to get even with the stations," he said.
Meanwhile ICTV general director Olexander Bohutsky advised care in view of the large numbers of Russian-speakers in the country.
However, the broadcasting council has promised not to neglect the interests of minorities. Local radio and television stations will have the right to broadcast in Russian if they can prove they have a Russian audience.