Labor unions are taking to the airwaves to fight Proposition 32, the November ballot measure that promises to eliminate special-interest money in politics.

Unions representing teachers, firefighters and state workers are airing statewide radio ads this week that cast the initiative as "a deceptive proposition stuffed with special exemptions for the oil companies, Wall Street and those secret campaign super PACs who want to rig the system while the middle class pays the price."

Proposition 32 would prohibit both unions and corporations from contributing directly to candidates. The initiative would also ban the practice of political contribution by payroll deduction, a provision that labor leaders say would disproportionately harm unions since that is the primary method labor organizations use to raise political cash.

Good government groups, including the League of Women Voters of California and Common Cause, also oppose the measure.

The "Yes on 32" campaign counters that the payroll provision is a way to "empower employees" and union members. Supporters say that if the measure passes, employees would still be able to make political contributions to their employer or union as long as the money is not automatically deducted but given with written consent.

The proposition's backers also dispute the claim that the measure includes special exemptions. The initiative, they say, uses language that mirrors federal law and bans all corporations from giving directly to candidates.

Proposition 32 is labor's top priority this year. So far, the union-backed opposition campaign has raised more than $17.7 million.