Ukrainian lawmakers have filed a challenge to a law that allowed newly elected President Viktor Yanukovych to cement his grip on power.

Yanukovych's party built a new majority coalition this week that attracted deputies from rival factions, including several defectors from ex-Prime Minister Yulia Tymoshenko's bloc.

The parliament then quickly approved an ally of Yanukovych as the new premier.

Before forming the coalition, Yanukovych signed the law allowing individual deputies to break away from their factions. Opposition lawmakers argue it is unconstitutional because the constitution only allows entire factions to join a coalition.

The Constitutional Court said Friday it had received the claim filed by 56 lawmakers. No date for a hearing has been set.