A group trying to block a new law expanding Medicaid by collecting enough signatures to put it on the ballot plans a kick-off event at the Arizona Capitol.

The 10 a.m. Saturday rally organized by opponents of the new law is expected to draw lawmakers and party activists from across the state.

Christine Bauserman of the United Republican Alliance of Principled Conservatives says they'll hand out petitions and then head to the Phoenix-area districts of two key Medicaid supporters, Rep. Heather Carter and Sen. John McComish.

Gov. Jan Brewer pushed the law through the Legislature and signed it Monday. It will add about 300,000 poor Arizonans to the state's Medicaid plan.

The group must collect 86, 405 valid signatures by Sept. 11 to get it on the November 2014 ballot.