Mr Netanyahu's supporters have been campaigning heavily for him, amid concerns that a low turnout could boost his rival's support.
Mr Feiglin, a hardliner, has described a future Palestinian state as "a terrorist country right in the heart of the land of the Bible".
Although he is not expected to win, a strong showing in the primary vote would be an embarrassment to mainstream Likud.
Yaron Ezrahi, a political analyst, said that if Mr Feiglin secured more than 30 per cent of the votes, it would seriously hurt Likud's image.
