JERUSALEM - Israel's powerful defense minister on Thursday said his Labor Party would lead a motion to dissolve parliament later this month, stepping up pressure on the ruling Kadima Party to replace Prime Minister Ehud Olmert as he battles a corruption scandal.

Defense Minister Ehud Barak, whose Labor Party is Kadima's main coalition partner, has previously threatened to topple the government if Olmert didn't step aside. But Thursday's threat to take parliamentary action on June 25 was the first time he had set a deadline for Kadima to act.

"We prefer governmental stability to elections," Barak told his party on Thursday. "But the way things look now, we will join - in fact, lead - a proposal to dissolve parliament on June 25."

Israeli police are investigating hundreds of thousands of dollars in donations given to Olmert in the years before he became prime minister in 2006. Olmert has denied any wrongdoing and promised to resign if indicted.

However, he has faced growing calls to resign since the key witness in the case, a Jewish American businessman, testified last month that he had delivered some $150,000 in cash-stuffed envelopes to Olmert, in part to pay for the lavish tastes of the Israeli politician.

A number of opposition parties have already said they plan to submit motions to dissolve parliament. With Labor's support, the motion stands a far greater chance of passing. Labor is Kadima's main coalition partner, and Olmert's government would lose its parliamentary majority without it.

Dismantling parliament likely would mean moving up elections, now scheduled for late 2010. Barak has said he would keep Labor in the government if Kadima replaced Olmert as party leader.

Kadima has agreed to start readying for a leadership primary, though no date has been set. But that apparently did not satisfy Barak, a former prime minister with an eye on reclaiming his old job.

The June 25 vote would not decide Olmert's political future, but it would be a barometer of parliament's sentiment. Any bill to dissolve parliament would later have to be put to three parliamentary votes.

Olmert spokesman Mark Regev had no comment on Barak's remarks. But Kadima lawmaker Tzahi Hanegbi, who is helping to set plans for a party primary, told Army Radio that "the die is cast. We're going to elections."

Polls show that Olmert's top rival in Kadima, Foreign Minister Tzipi Livni, is popular with the public. But if elections were to be held today, most surveys would hand the premiership to Benjamin Netanyahu of the opposition Likud Party, who opposes the sweeping territorial concessions that any peace deal with the Palestinians would require.