KIEV, June 15 - A group of pro-government lawmakers on Saturday appealed to the Constitutional Court seeking cancellation of President Viktor Yushchenko's decree scheduling early elections on Sept. 30.

The move, which may trigger a new wave of political confrontation, came a day after at least 151 opposition lawmakers officially quit their seats in Parliament to open way for the election.

The appeal challenges a political agreement between Yushchenko, a pro-Western leader, and Prime Minister Viktor Yanukovych, a pro-Russian leader, aimed at ending the sharpest political crisis in Ukraine since the November 2004 Orange Revolution.

"The appeal does not fit the political agreement that had been reached," Viacheslav Kyrylenko, the leader of Our Ukraine, an opposition party, said. "The president sticks to the agreement, but the members of the coalition have begun to torpedo the election."

Yushchenko, Yanukovych and Parliament Speaker Oleksandr Moroz agreed two weeks ago to end the sharp political crisis by making a deal that had supposed to lead to the dismissal of Parliament and for holding the election Sept. 30.

According to the deal, at least 151 opposition lawmakers had to quit their seats in the 450-seat Parliament to make way for the election. But Moroz, and later Yanukovych, later questioned whether so many lawmakers would actually quit the legislature.

A new twist came on Friday when all opposition lawmakers confirmed their intention to quit the legislature, triggering an angry reaction from Moroz, people familiar with the situation said.

This was quickly followed by the appeal from 55 lawmakers, members of the coalition, seeking to cancel Yushchenko's decree.

"The members of the coalition until the last moment could not believe that more than 150 opposition lawmakers would quit their mandates," Kyrylenko said. "Now, they decided to backpedal on the deal."

The developments come amid other signs that the coalition has been seeking to undermine the political agreement, including allegedly sabotaging the Central Election Commission.

"There is a threat that the election will be undermined. We have to talk about it," Volodymyr Shapoval, the chairman of the committee, said on Friday.

The 15-strong commission is currently split between eight loyalists of Yanukovych and seven loyalists of Yushchenko.

Shapoval, a Yushchenko loyalist, for the past week has been refusing to hold a meeting by the commission amid fears that the commission would approve a decision that could undermine the election.

For example, Shapoval said the commission, dominated by Yanukovych loyalists, would approve a decision to add more lawmakers Parliament, replacing those that had just quit their seats. This would de-facto undermine the dismissal of Parliament and the early election, Shapoval said.

"If from the very beginning we start to solve issues on the principle that 'There are eight of us,' then there will be two commissions," Shapoval said. (tl/ez)