Pandora is currently lobbying lawmakers in US Congress to pass the “Internet Radio Fairness Act,” which would change regulation of how royalties are paid to artists. A group of 125 musicians who say they are fans of Pandora argue the bill would cut by 85 percent the amount of money an artist receives when his or her songs are played over the Internet. “Why is the company asking Congress once again to step in and gut the royalties that thousands of musicians rely upon? That’s not fair and that’s not how partners work together,” said the letter, to be published this weekend in Billboard, the influential music industry magazine. A statement with an advance copy of the letter was released on Wednesday by musicFirst, a coalition of musicians and business people, and SoundExchange, a nonprofit organization that collects royalties set by Congress on behalf of musicians. “Internet radio and the artists whose music is played and listened to on the Internet are indeed all in this together,” Tim Westergren, Pandora’s founder and chief strategy officer, said in a statement.