So far, two local administrations -- the eastern region of Luhansk and the city of Sevastopol, in the Crimea -- have tried to elevate the status of Russian.
Both regions have a predominantly Russian-speaking population.
Yushchenko's deputy chief-of-staff, Anatoliy Matviyenko, said on April 28 that the moves breach Ukraine's constitution, which states that Ukrainian is the sole state language.
The status of the Russian language has become one of the most politically divisive issues in Ukraine.
The pro-Moscow Party of Regions, which won the most votes in last month's parliamentary election, campaigned on a promise to make Russian a second state language.
(Interfax-Ukrayina, Ukraiynska pravda)