Opposition leader Yair Lapid says Yamina has informed him it will support a no-confidence motion aiming to topple the government next week.
There is no immediate confirmation from the nationalist party, whose five seats will not be enough to push Lapid’s bid over the edge.
“If Blue and White votes for it, we can switch out this failing government for one that will take care of the million unemployed and businesses falling apart,” Lapid says in a tweet.
The right-wing Yamina has vacillated between supporting and opposing or abstaining from a series of failed no-confidence bids pushed by Lapid.
Party leader Naftali Bennett, whom polls show as the strongest challenger to Prime Minister Benjamin Netanyahu, has said he will make a run for prime minister in upcoming elections after a falling out with the Likud leader.
The coalition has teetered in recent days as ties between Netanyahu and Blue and White head Benny Gantz have been frayed to nearly the point of breaking off completely.
The no-confidence vote is scheduled for December 2.