NEW YORK — Rush Limbaugh’s opponents are starting a radio campaign against him Thursday, seizing upon the radio star’s attack of a Georgetown law student as a “slut” to make a long-term effort aimed at weakening his business.

The liberal Media Matters for America is using a past campaign against Glenn Beck as a template. In Limbaugh, however, they’re going after bigger game. He’s already fighting back and the group’s stance has provoked concerns that an effort to silence someone for objectionable talk is in itself objectionable.

Media Matters is spending at least $100,000 for two advertisements that will run in eight cities.

The ads use Limbaugh’s own words about student Sandra Fluke, who told congressional Democrats that contraception should be paid for in health plans. Limbaugh, on his radio programs, suggested Fluke wanted to be paid to have sex, which made her a “slut” and a “prostitute.”