Prime Minister Benjamin Netanyahu is demanding full control of Israel's Iran policy as Joe Biden prepares to assume the Oval Office, setting off a fierce fight at the highest echelons of Israel's government, senior Israeli officials tell me.

Why it matters: Prime Minister Benjamin Netanyahu is preparing to take a very hard line over Biden's plan to return to the 2015 nuclear deal, in contrast with the more moderate approach favored by Defense Minister Benny Gantz, Foreign Minister Gabi Ashkenazi and the heads of Israel's security services.

Driving the news: On Dec. 29, under orders from Netanyahu, Israeli national security adviser Meir Ben Shabbat sent a one-sentence letter to Gantz:

Axios obtained the contents of the letter, which was also sent to Ashkenazi, Israeli ambassador to Washington Ron Dermer, Mossad director Yossi Cohen and IDF chief of staff General Aviv Kochavi. No explanation was provided as to the timing of the letter or why it was sent, Israeli officials tell me.

Behind the scenes: Gantz was stunned by Netanyahu’s letter and replied two days later with a letter of his own. Gantz wrote that the prime minister does indeed have the authority to finalize Israel's position, but not to disregard almost the entire security establishment and intelligence community while also bypassing Israel's security cabinet.

Gantz added that Israeli policy on the Iran deal must be the result of a broad analysis involving all of Israel’s national security and foreign policy agencies, rather than just the national security council, which reports directly to Netanyahu.

• Gantz also wrote that any such policy must be approved after a serious discussion in the security cabinet.
• Before today, the confrontation between Netanyahu and Gantz was known only to a small group of very senior national security officials.

Between the lines: The timing of the argument — a few weeks before Biden assumes office, and in the midst of Israel's election campaign — makes it even more sensitive and dangerous.

• While all of the key players agree on the strategic goal of preventing Biden from agreeing to a deal that harms Israeli security, they disagree on tactics.

Hanging over the process is the fact that Netanyahu's emphatic rejection of any deal in 2015 effectively sidelined Israel as Barack Obama sealed the previous deal. That's led some senior officials to seek a a more collaborative approach with the U.S. this time.

• One Netanyahu adviser tells me Netanyahu was motivated to send the letter by an interview in the Israeli press in which the retiring head of Israel's military intelligence research department said there was no proof that President Trump’s withdrawal from the deal served Israel’s interests.
• Netanyahu was also upset by rumors that during the visit of U.S. Joint Chiefs Chairman Gen. Mark Milley, Gantz and several senior Israel Defense Forces generals voiced a more moderate position on the Iran deal.

Worth noting: Netanyahu and Gantz declined to comment for this story.