The former general told Army Radio on Thursday that Knesset members "cannot be for me but against the plan I am spearheading".
Many of the 193,000 Likud members have been lobbying the PM intensely over his plan to remove 21 illegal Israeli settlements in occupied Gaza.
But newspaper polls project he could lose a key referendum on Sunday.
Sharon stopped short of ultimatums, but Israel Radio's political correspondent said he may use a threat to resign his post as a "doomsday weapon" to sway Sunday's vote.
Sharon's success in winning over party hawks hinges on US President George Bush's declaration this month that Israel may keep various illegal settlements in the occupied West Bank.
Bush also backed Tel Aviv in not allowing Palestinian refugees or their descendants to return to land or property taken by force in 1948 and 1967.
Israel has built 21 illegal colonies
on occupied land in Gaza
But the right-wing Likud shows little sign of abandoning its longstanding policy of holding on to "Greater Israel", including the occupied Palestinian territories.
Meanwhile, the Israeli PM may have cause to celebrate a minor success in an on-going investigation into alleged corruption.
A television report claimed an interim legal report had found that Israeli prosecutors lack evidence to charge him in a bribery scandal.
The case centres on payments of hundreds of thousands of dollars by an Israeli land developer and Likud stalwart to Sharon's son Gilad, whom he hired as an adviser on a never-completed project to build a resort in Greece.
A focus for prosecutors was whether Sharon, then foreign minister, tried to help win Greek government approval for the enterprise, promoted by Likud kingmaker David Appel, now on trial on related bribery charges. Sharon denies any wrongdoing.
The Justice Ministry said a final decision was still pending.