According to this story, the Republican Party of Jefferson County, West Virginia, seems to feel that it might be illegal for anyone running in a Republican primary to communicate with Democratic voters, asking them to switch their registration from Democratic to independent so as to be able to choose a Republican primary ballot and vote for the candidate who asked them to switch. Independents can vote in major party primaries in West Virginia.
The Republican candidate who did this has a primary opponent, and the opponent is on the Republican Party County Committee.