The only ground they have to stand on is the legal one. If they used the song without permission (if required) then I agree with the cease and desist letter. If it's out of principle because of their political beliefs, it's downright petty.
I have to disagree - If the song is available for sale, and if it can be played publicly as long as royalties and other fees are paid, I cannot see political affiliation as any valid disqualifier for usage.
What would happen if, Lets say, Limbaugh only allows people to purchase his latest book after displaying proof of Republican party membership, and denied everyone but Republicans from printing or airing a review on it ?
Cries of Censorship! Fascist! etc etc etc from the left.. that's what. But according to Heart, since this is Rush's work, this is his right, regardless of the willingness to attain the copyrighted work legally.