Pandora Media Inc., the money-losing Internet music service, has almost 60 million listeners to enlist for support while lobbying Congress for help to lower the royalties it pays to musicians.

Rihanna’s Facebook page can top that, with 63 million fans. And the 24-year-old singing superstar, whose “Diamonds” is No. 1 on Billboard magazine’s Hot 100, is just one of 125 artists who this month went public to oppose Pandora’s bid to cut fees for performers.