From JPost, 28/5/08:
Prime Minister Ehud Olmert will not quit despite the illicit funding investigation against him, since such a move wound be tantamount to an admission of guilt, the prime minister's strategic adviser, Tal Zilberstein, said Wednesday.
It followed reports that Defense Minister Ehud Barak planned to present Olmert with an ultimatum at a press conference on Wednesday afternoon: Either the premier resign, or Labor will pull out of the coalition, thus forcing new elections.
...and from Ynet News, 28/5/08:
Barak was expected to hold a special conference at 1:30 pm Wednesday and to address the issue.