A Kroger supermarket didn’t violate federal labor law when it called the police to force a union activist to stop soliciting in the store’s parking lot and leave the area, the National Labor Relations Board ruled Sept. 6.

Kroger’s enforcement of its no-solicitation rule and subsequent efforts to eject the union weren’t discriminatory even though the store regularly allowed several charitable organizations to solicit on its property, the labor board said in its 3-1 ruling. The NLRB overturned its 1999 ruling in Sandusky Mall that required employers to allow unions on their property if they give access to groups for...