Eleven members of two "orange" opposition blocs - pro-presidential Our Ukraine and the Yulia Tymoshenko Bloc - joined the ruling coalition March 23, further aggravating the political crisis in the former Soviet nation.
"Individual defections have given way to mass reinforcement of the coalition, which contradicts the Constitution," President Viktor Yushchenko, who came to power in 2004 on the back of the "orange revolution" in alliance with Tymoshenko, said in a letter to the Supreme Rada.
Yushchenko cited the Constitution as saying the parliamentary majority must be based on election results, and cannot be changed afterwards.
"As a guarantor of state sovereignty, territorial integrity of Ukraine and the Constitution, and also individual rights and freedoms, I cannot turn a blind eye to the destructive processes, and must demand that the Supreme Rada stop defying constitutional provisions," Yushchenko said, adding the situation distorted election results.
The Ukrainian leader warned he would be forced otherwise to "take adequate measures to stop such unconstitutional actions."
Parliamentary elections in Ukraine in March 2006 saw the Party of Regions come first, followed by the Tymoshenko Bloc and Our Ukraine. The Party of Regions, the Socialists and Communists formed a majority coalition after five months of political wrangling, and elected Viktor Yanukovych prime minister.
Constitutional amendments adopted in the wake of the "orange revolution" transformed the country from a presidential into parliamentary republic, which sparked a power struggle between the president and prime minister.
"The developments have put in doubt the Cabinet's legitimacy, whose ministers have recently been appointed by the ruling coalition in violation of the Constitution," the president said.
The opposition has said it would hold protests on the central square of Kiev, Maidan, Saturday to demand that parliament be dissolved and early elections called.
"Protests by the united opposition including Our Ukraine, the Yulia Tymoshenko Bloc and People's Self-Defense will be held in Maidan at 5 p.m. [2 p.m. GMT] Saturday," an Our Ukraine representative said.
Prime Minister Yanukovych, an arch rival of Yushchenko in the 2003 presidential race, said the ruling coalition led by his Party of Regions already had 260 members in the 450-seat parliament.
Parliamentary Speaker Oleksandr Moroz said he expected the parliamentary majority to reach 300, which would make up the constitutional majority.
