Just days after the top machine workers union endorsed Hillary Clinton’s presidential campaign, many of its members are lashing out at the leadership for declining to back Democratic challenger Bernie Sanders, In These Times reports.

Last Friday, the International Association of Machinists and Aerospace Workers (IAM) joined the American Federation of Teachers by announcing its support for Clinton, who has deep ties to Wall Street financial interests.

The decision angered many of the IAM’s members, who took to the union’s Facebook page to lobby for Sanders:

"I cannot describe how disappointed I am with the IAM endorsing Hillary," says Al Wagner, a journeyman auto technician and member of IAM Automotive Mechanics Local 701 in Chicago. "The IAM is a great union and I am very proud to be a member. But the leaders went about this endorsement the wrong way." … "Awful choice! I'm with Bernie," wrote one person claiming to be a member on the union's Facebook page. "What a sham! Not in the least bit democratic … — only 1700 out of 500,000 members is not a majority. … At monthly meetings, members talk about the real voice of labor (Bernie Sanders) who BTW is beating her in the CNN [poll] after every meeting. You guys need to wake up and listen to your members," wrote another.

In These Times noted that "Sanders’ popularity—and the post-Clinton-endorsement outcry—within IAM should not be surprising. Since 1989, the union’s political action committee has been the Vermont Senator’s top campaign contributor. Clinton, on the other hand, is currently facing all-time lows in her favorability among voters."

IAM defended its decision by saying it took an internal survey of its membership and 71 percent supported Clinton. However, critics questioned the validity of the IAM’s polling and the sample size.

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Update: 5:22 P.M.: A previous version of this article said that the National Nurses United union endorsed Hillary Clinton. They endorsed Bernie Sanders.