Jerusalem ? A day after embarrassing testimony about his receipt of cash envelopes from a U.S. businessman, Israeli Prime Minister Ehud Olmert came under increased pressure to resign Wednesday when a key coalition partner, Ehud Barak, called on him to step aside or face the collapse of his government.

Barak, the defense minister and former prime minister, said that if Olmert did not relinquish his duties, Barak’s Labor Party would force new elections.

Though Barak did not set a deadline, the threat raises the prospect of a change of leadership that could disrupt Israel’s renewed peace talks with Syria and Washington’s efforts to achieve an Israeli-Palestinian accord before President Bush leaves office.

“It should happen soon, and I mean soon,” said Barak about his demand that Olmert step aside.