MADISON, Wis. — Liberal rocker John Mellencamp wants conservative Republican Gov. Scott Walker to know he supports union rights and says Walker should think about that before using his songs on the campaign trail.

Politicians for years have been using rock songs at campaign events, and Mellencamp has found himself crossways with Walker and other candidates before.

Two years ago, Mellencamp chided Walker, who effectively ended collective bargaining for most public workers in Wisconsin, for playing his song “Small Town” at campaign rallies.

Mellencamp took the same approach in 2008 when Republican presidential hopeful John McCain played “Our Country” on the campaign trail.

When Walker launched his re-election campaign with a series of rallies Tuesday, one of the songs played while his supporters waited for the governor was “Pink Houses.” The song, first released in 1983, contains the lyrics, “Ain’t that America, home of the free. Little pink houses for you and me.”

Mellencamp has not directly contacted Walker’s campaign this year about his use of the song, said the rocker’s publicist Claire Mercuri. But Mellencamp wants to again let Walker know about his support of unions and collective bargaining.