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All the other candidates are either confirmed speakers or have said they will be accepting their invitation to speak

AIPAC has a tradition of inviting all the presidential candidates in election years to the conference

(CNN) —  

Bernie Sanders isn’t attending a major pro-Israel conference in Washington this week.

Sanders, the first Jewish politician to ever win a presidential primary, is the only remaining 2016 contender who will not speak at the American Israel Public Affairs Committee, a major gathering for politicians and Jewish leaders every year.

In a letter to AIPAC President Robert Cohen, Sanders expressed regret that he could not attend the annual conference, but said “issues impacting Israel and the Middle East are of the utmost importance to me, to our country and to the world.”

Sanders said he was scheduled to be traveling throughout the West and his campaign schedule prevents him from attending. He said he would send remarks to the organization in the hopes that they could be distributed to members as AIPAC does not permit candidates to address the conference remotely.

Sanders’ opponent, Democratic front-runner Hillary Clinton, will be a featured speaker.

AIPAC has a tradition of inviting all the presidential candidates in election years to the conference. In fact, Donald Trump’s attendance this year has drawn backlash from attendees, some of whom plan to boycott his speech on Monday.

RELATED: Rabbis plan boycott of Trump at AIPAC

A petition started by Max Blumenthal, the son of former Clinton adviser Sidney Blumenthal and a pro-Palestinian writer, had garnered more then 5,000 signatures urging Sanders not to speak at AIPAC. One of the signers is Pink Floyd musician Roger Waters, who has endorsed Sanders.

On the other hand, foreign policy writer Robert Naiman wrote an open letter to Sanders encouraging him to speak at AIPAC – urging him to be a “truth-teller” to the group. Naiman is critical of the group’s hard-line pro-Israel stance.

AIPAC lobbies politicians on its pro-Israel agenda and energizes Americans around strengthening the U.S.-Israel relationship. Its annual conference is a must-stop for politicians every year looking to appear before the influential audience.

The group has also been a source of criticism for the anti-Zionist and pro-Palestinian movement in the U.S., as well as other pro-Israel groups who believes AIPAC takes too rigid a stance against the Iran nuclear deal.

Though Sanders won’t be at AIPAC, he will be delivering a foreign policy speech on Monday. His campaign announced Sunday evening that he will give a major address on international affairs, in Salt Lake City on Monday. The Utah Democratic caucuses are on Tuesday.

CNN’s Elizabeth Landers contributed to this report.