The United Republican Alliance of Principled Conservatives must file them by Sept. 11 to block the law approved by the Legislature and signed by Republican Gov. Jan Brewer in June. Conservative Republicans strongly opposed the law.
A successful filing will block the law until a November 2014 election.
The group has been collecting signatures using volunteers since June. Organizer Christine Bauserman says they're excited to have the large infusion of cash. She says she doesn't know if paid signature gatherers will now be hired.