Muhammad Shahran, who heads the 12-member Baiji Higher Electoral Commission, said on Sunday that the people issuing the threats declared the election illegitimate because it would occur under occupation.
Two committee members had already resigned two months ago.
The main Electoral Commission in Baghdad could not immediately be reached for comment.
Anti-US fighters are active in Baiji, home of Iraq's biggest oil refinery.
They have been mounting relentless attacks against US and Iraqi forces in the town, and on those working for them.
The fighters have also severely disrupted the import of goods and refined oil products from neighbouring Turkey.
Anti-US fighters are active in the
oil town of Baiji
Earlier on Sunday, fighters in the nearby town of Sharqat ordered municipal workers out of a local government building serving as a polling centre, before blowing it up.
The resignations come after the entire staff of Iraq's Independent Electoral Commission in the northern city of Mosul - around 700 employees - resigned last week.
Staff members said their resignations followed threats they had received.
Iraqi officials say election preparations in the country's mainly Sunni west and north are lagging because of violence. Arab Sunni clerics have urged a boycott of the polls.
The elections, for a National Assembly that will appoint a government and draft a permanent constitution, are expected to be dominated by Shia groups who are keen to cement their increased power following the fall of Saddam Hussein.