Gantz left the opposition to join Netanyahu in a mini-war government shortly after a Hamas militant offensive on southern Israel last month sparked the war in Gaza.
Although he is a member of the cabinet, Gantz did not hesitate to attack Netanyahu, especially when he criticized the heads of Israel's intelligence services for the Hamas attack.
But the budget issue may have real consequences that could end the fragile arrangements imposed by the Hamas offensive that brought together centrist Gantz and Netanyahu's far-right partners, including Finance Minister Bezalel Smotrich.
Under Netanyahu's alliance deal with Smotrich and leaders of other religious parties after last year's elections, billions of dollars are set to go to ultra-Orthodox and far-right pro-settler parties.
In a strongly worded letter to Netanyahu released by his office, Gantz referred to a broader cabinet meeting scheduled for Monday to discuss proposed budget adjustments.
Gantz reiterated his opposition to including "coalition funds" in the proposed budget, saying no additional funds should be allocated for purposes beyond the war effort or supporting economic growth.
If the meeting takes place with the budget remaining in its current state, Gantz said his party would "vote against the proposed budget and consider its next steps."
- Netanyahu's office said he would put the budget to a vote on Monday and played down Gantz's criticism, adding: "This political controversy concerns about one percent of the total budget."
- Most of the coalition's funds have been reduced and the remaining funds have nothing to do with politics, the office said.
- The Central Bank of Israel criticized the proposed budget adjustments, saying the cuts were not enough and that the government should show more fiscal responsibility when dealing with the economic impact of the war.