The state supreme court rules they have to abide by Maine's laws for disclosing their out-of-state donors. Here's the PDF ruling. Money quote:

Maine is entitled to conclude that its electorate needs to know, on an ongoing basis, the source of financial support for those who are taking positions on a ballot initiative. It will not do to say that a one-time disclosure in the week before the election is sufficient. That would not give the opposing viewpoint the opportunity to point out the source of the financing and seek to persuade the electorate that the source of support discounts the message.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.