A federal appeals court ruled Tuesday that nonprofit “social welfare” groups that spend money on campaign advertising can keep their donors secret, reversing a lower-court decision that mandated some disclosure, according to Reuters and the Associated Press.

A three-judge U.S. Court of Appeals panel unanimously overturned federal District Judge Amy Berman Jackson’s March ruling, which had forced politically active 501(c)(4) to change their advertising strategies to continue shielding donors’ identities.

Judge Jackson ruled that the Federal Election Commission violated the intent of congressional campaign-finance legislation in 2007 when it narrowed disclosure requirements for such organizations. But the appeals court said the law, known as McCain-Feingold, is “anything but clear” on the issue and instructed Judge Jackson to refer the case back to the FEC.

Political activity by 501(c)(4) groups has been a contentious and largely partisan campaign issue, with primarily conservative organizations spending tens of millions of dollars on ads. Democrats and watchdog groups urge tighter regulation and disclosure requirements, which Republicans contend would impinge on free speech.