a third of a party can quit - that it the crazy law we have - not a specific number. That is why Israeli politicians have no respect for the people who elected them. Once they are in their seats - anything goes. the law needs to be changed so that if someone wants to quit his party, he has to return the mandate.
Justice Ministry: Information examined by AG about Gal Hirsch didn't come from police (Haaretz)
from the article: Barak's Atzmaut faction receives four portfolios in coalition government