Likud leaders were putting heavy pressure on party activists to attend the rally today evening in Tel Aviv.
Hundreds of supporters packed a Tel Aviv convention center ahead of Netanyahu's expected speech. Some supporters held signs and chanted "Bibi, King of Israel," using the prime minister's nickname.
Party leaders described it as an attempt to counter a vicious campaign by a hostile media and overzealous police and state prosecution. But the gathering was also serving as a test of Netanyahu's popularity and control over his party.
"This gathering is important to unify the ranks in the party in support for the prime minister and raise the morale of party activists," he told Army Radio.
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"There is a really difficult feeling in the Likud. There is a feeling that things are not being conducted fairly and the influence of the left on the process is serious."
Israeli police investigators say they suspect Netanyahu of being involved in bribery, fraud and breach of trust in a pair of cases.
Netanyahu's former chief of staff and longtime confidant, Ari Harow, recently signed a settlement connected to a separate case in which he agreed to testify against his former mentor.
This has raised speculation that Netanyahu could be indicted soon, and has sparked opposition calls for him to step down.
Bitan said some 1,500 were signed up for the event and he hoped even more would attend including all the party's top officials and ministers.
Netanyahu is expected to address the gathering, as long as the turnout is as impressive as hoped. No one in the party has come out against Netanyahu yet reflecting both loyalty and the fear of crossing him.
Netanyahu's primary potential heir, Cabinet minister Yisrael Katz, has said he will attend the event and is expected to offer broad backing. A close eye will be kept on those who skip it.