It’s no secret that labor unions are struggling. Even though federal law tilts decidedly in their favor, unions have seen their share of the workforce steadily decline. Membership has been dropping, both in total numbers and as a percentage of the workforce, for many decades. Only 1 in 10 American workers is now unionized, and in the private sector, the unionization rate is less than 6%.

Yet instead of trying to persuade workers to sign up, unions have settled on a more coercive strategy: activist investing that endangers union members’ retirement funding.