Turkey's state television has banned the main opposition party's election campaign advert because it directly targets the government.
The Republican People's Party (CHP) accused broadcaster TRT of "abusing public office" and vowed to take legal action.
It has previously protested at TRT "bias" towards President Recep Tayyip Erdogan and his Justice and Development Party (AKP).
The election will take place on 7 June.
In a statement on the CHP website (in Turkish), deputy leader Bulent Tezcan said: "By taking the decision not the broadcast the advertisement, TRT has created a new scandal.
"The main purpose of state-funded television in all democratic countries is fairness of broadcasting. TRT's direction are committing the crime of abuse of public office," he added.
Mr Tezcan also reminded the broadcaster that it is "owned by the public".
TRT has so far declined to comment.
The opposition advert featured the slogan "we applaud as a nation" and criticised the "oppression" of justice, freedom and secularism in the country.
It urged voters to attend the party's first mass election rally on Saturday.
The controversy follows a ruling by a court in Ankara on Thursday, which ordered CHP leader Kemal Kilicdaroglu to pay damages for insulting President Erdogan in a speech in 2013.