Bernie Sanders's supporters are known to be very vocal and aggressive on Twitter.
They've been accused of harassment and vicious personal attacks online.
Now, Sanders is stepping in, begging supporters to stop their online harassment.
On Thursday Sanders urged an end to online "bullying or ugly personal attacks."
Sanders isn't doing this out of the goodness of his heart.
He's making the plea to his supports because their behavior could cost him the nomination.
A powerful powerful hospitality-industry union in Nevada accused his supporters of harassment.
The Culinary Workers Union said supporters of Sanders viciously" attacked the organization.
They say they've been bombarded by Twitter, text, voicemail and direct messaging.
The attacks came after the union criticized the senator's universal healthcare plan on Tuesday.
Sanders only stepped in after the union's endorsement was threatened.
"Anybody making personal attacks against anybody else in my name is not part of our movement.
We don't want them."