Petitioners must report income or pay Business & Occupation taxes if they remain independent.
We know that paid signature gathering is a cash business by nature, and that many mercenaries are drawn to the profession not just because of the earning potential, but also because it is untaxed work. Many mercenary petitioners do this work because they make good money without paying taxes or having any relationship with government agencies that observe employment status and levy taxes based on that. They are almost universally independent contractors and are not employed by the vendors who sign the contracts with funders to qualify initiatives.
Since petitioners operate as independent contractors and the industry works on a cash basis by design, one potent angle for reform is requiring that petitioners pay Business & Occupation taxes. This is only possible if they are registered with the state, which we want to do for other reasons as well. This means that they'd be required to pay taxes rather than essentially working under the table. It would place some burden on the sub-contractors who administer the cash, which is fine. If a petitioner has failed to pay B&O taxes and owes a state money s/he could be required to pay back taxes before being allowed to petition again.
Currently there is no state that extends B&O taxes to paid signature gatherers.