Shalom made the statement during a press conference in Tel Aviv, where he announced his withdrawal from the race for Likud chairman.
"The move Bibi planned is not elections nor primaries, but an opportunistic step with which I cannot cooperate. This is an illegitimate move from a public perspective," he added.
Likud Chairman Benjamin Netanyahu decided last week to push up the Likud internal elections to September, despite opposition from Shalom, who wanted primaries to be held after Rosh Hashana in order to enable candidates to prepare.
"Today could have been the Likud's finest hour. We could hold a brief and fair campaign. But what we will have instead is a charade, a procedure that is a pseudo-campaign, and therefore I cannot take part in this.
"The coming primaries will be between Bibi and (Moshe) Feiglin, and may the best man win."
Moshe Feiglin is head of the extreme-rightist Manhigut Yehudit (Jewish Leadership) faction in the Likud. In 2005 Feiglin ran for Likud chairman and won 12.5% of the votes.
According to Shalom, a true primaries campaign should allow contenders to present their agenda to the voters, a process that cannot be achieved in such a short period of time.
Shalom also accused Netanyahu of aggressive behavior that was driving members and voters away from the Likud. "No one, not even Bibi, will drive me out of my home. I was here before him, and I will stay in the Likud after him," he stated.
In response to Shalom's speech, Netanyahu's aides said, "Shalom explained his decision using lame excuses of someone who is about to be defeated."