The League of Women Voters of California and Common Cause are urging the defeat of Prop 32, which would ban corporations and labor unions from directly contributing to candidates.
Trudy Schafer, with the League of Women Voters, says the measure isn't about political reform.
She says it would exempt thousands of big businesses including Super PACS and Limited Liability corporations.
Schafer: "It promises political reform, but it's really designed by its special interest backers to help themselves and harm their opponents."
But Jake Suski, of the Prop 32 campaign, says the measure uses federal and state definitions of corporations.
SUSKI: "Prop 32 applies to every corporation, it's simple, it's in the language, as for how it will be implemented that's going to be up to state law and the courts to decide."
The measure would also ban the practice of deducting political contributions from paychecks, which is the primary way labor unions raise political money.