TAMPA, Fla. — Former Massachusetts Gov. Mitt Romney's Republican rivals have yet to begin running television ads in Florida, but a labor union is spending almost $1 million on a new ad attacking the GOP front-runner's business career.

The American Federation of State, County and Municipal Employees will begin airing the anti-Romney ad Saturday on television stations across central Florida. It'll run through the state's Jan. 31 presidential primary.

The ad links Romney's time heading Bain Capital to corporate greed and Medicare fraud. That's a similar line of attack employed by Romney's Republican opponents elsewhere.

The ad is believed to be organized labor's first major investment in the GOP presidential primary. The union's political director says that Florida represents the last best chance to stop Romney's march toward his party's presidential nomination.