Their letter claims that “faulty” audience measurement had placed radio stations serving black and Hispanic audiences “in the worst possible situation in their fight to weather the economic storm”.

Signed by members of the National Association for the Advancement of Colored People, the Minority Media and Telecommunications Council and the Hispanic Telecommunications and Technology Partnership, the letter stated: “Without the immediate intervention of the federal government, we stand to lose a valuable and irreplaceable resource – the independent voice of minority radio.”

Minority broadcasters have long complained that their audiences are under-represented in the sample for Arbitron’s portable people meter (PPM) system, as a result of which their audiences are undercounted and their ad income suffers.

Arbitron has yet to comment on the letter, though its CEO said recently that the representation of Black and Hispanic groups in the PPM sample was “strong”.

The company has also previously said that differences between listening figures from the PPM system and the paper diary-based method it replaces are because PPM measures actual listening, while diaries only measure recall and loyalty.

Last month ten congressman wrote to the Government Accountability Office to press for an investigation of PPM and to examine its impact on minority radio. The Federal Communications Commission is also holding its own inquiry.

Obama, meanwhile, is not unsympathetic to the concerns of minority broadcasters. When he was an Illinois senator he wrote to Arbitron asking the firm to postpone commercialisation of PPM in Chicago until it had secured accreditation from the industry auditor the Media Rating Council.