It's not often union members are looking to back a Republican candidate for president, but some union leaders are worried Donald Trump may be the exception.

Mary Kay Henry, president of the Service Employees International Union, may have thrown her organization's weight behind Hillary Clinton, but Henry tells The New York Times that many members are attracted to Trump as they deal with anxiety over the state of the economy:

In expressing her concern, Ms. Henry reflected a different form of anxiety that is weighing on some union leaders and Democratic operatives: their fear that Mr. Trump, if not effectively countered, may draw an unusually large number of union voters in a possible general election matchup. This could, in turn, give Republicans a boost in swing states like Ohio, Pennsylvania, Michigan and Wisconsin, all of which President Obama won twice.

The source of the attraction to Mr. Trump, say union members and leaders, is manifold: the candidate’s unapologetically populist positions on certain economic issues, particularly trade; a frustration with the impotence of conventional politicians; and above all, a sense that he rejects the norms of Washington discourse.

The paper also spoke to leaders of unions representing construction workers, firefighters and others who are concerned that Trump could peel away support from their preferred Democratic candidate.

Richard Sabato of the construction trades council in northern New Jersey said his members know Trump for employing many unionized construction workers, and would likely support him on illegal immigration.