Opposition supporters and other opponents of a bill upgrading the status of the Russian language in Ukraine were rallying in Kyiv and other major cities on July 5 to protest the bill's apparent approval.
The majority Party of Regions rushed the bill through parliament two days earlier, sparking scuffles among lawmakers and between protesters and police.
Opposition figures have claimed the vote was conducted improperly and is therefore void.
Parliament speaker Volodymyr Lytvyn has tendered his resignation in protest at the bill's passage, which would allow the use of Russian in courts, education, and other government institutions in Russian-speaking regions.
The bill must be signed by the speaker of parliament as well as President Viktor Yanukovych, the head of the Party of Regions, to become law.
There were hundreds of protesters in the capital, Kyiv, but smaller numbers at demonstrations against the bill in cities like Kharkiv, Donetsk, and Dnipropetrovsk, according to RFE/RL's Ukrainian Service.
Language is a sensitive subject in Ukraine, whose state language is Ukrainian but where a significant number of people speak Russian as their mother tongue.
Based on reporting by AP and Interfax