AUGUSTA — Maine is set to collect data on how ballot campaign groups pay for petition signatures under a bill signed by Democratic Gov. Janet Mills.

Mills’ office says she signed the bill June 21. The Republican-sponsored legislation requires groups to provide the state a list of individuals paid to circulate petitions, and report the “method” of compensation.

Republicans critical of the influence of out-of-state advocacy groups have fought to reform Maine’s referendum process. Voters in recent elections have approved marijuana legalization, Medicaid expansion, minimum wage hikes and a ranked voting system.

The bill originally would have banned groups from paying circulators based on how many signatures they collect.

Mills previously signed a Republican bill requiring public hearings on ballot initiatives. The Maine Heritage Policy Center called it a “monumental victory for transparency.”