The National Farmers' Union Wales and an individual farmer have complained to the media watchdog about the charity's claims on culling.
"We have approached the RSPCA and launched a formal inquiry," said Matt Wilson, press officer at the ASA. "It could be contravening the advertising code in terms of substantiating its claims."
The Government is consulting until 10 March on whether it should sanction the killing of badgers to prevent the spread of bovine TB, a strain of tuberculosis that can be transmitted between cattle and other animals, including humans.
The RSPCA is urging people to send a letter, downloadable from its website, to the Department for Environment, Food and Rural Affairs (Third Sector, 8 February). The letter claims killing badgers could increase the spread of bovine TB and the best way to tackle the issue would be more routine testing of cattle. "This slaughter cannot be justified," the letter adds.
An RSPCA spokeswoman said: "We are confident all our ads comply with ASA standards."
- The ASA last week rejected complaints by 12 members of the public that a Scope advert showing a person in a wheelchair raising their middle finger was offensive. The watchdog said the advert "highlighted the difficulties and attitudes disabled people faced in using public transport".