Nearly 40,000 Verizon employees, members of the Communications Workers of America union, walked off the job Wednesday as part of one of the biggest strikes in recent U.S. history. The CWA is among Sanders' largest backers among organized labor groups.
"Tonight, I want to take my hat off to the CWA," he told supporters in the park. "They are standing up to a greedy corporation that wants to cut their health care benefits, send decent paying jobs abroad and then provide $20 million a year to their CEO."
A law enforcement official estimated the crowd size at 15,000, though the campaign cited a a higher number of attendees -- 27,000, according to a press release.
Earlier in the day, that CEO, Lowell McAdam, attacked Sanders in a long Linked-In post, calling the Vermont senator's "uninformed views" about his company "contemptible."
Sanders found a more welcoming audience below 8th Street in Manhattan, near New York University, where he was introduced by director Spike Lee and, before him, actress Rosario Dawson -- both New York natives.
Dawson took on Sanders' Democratic rival, Hillary Clinton, early in her remarks, saying, "too many people have died because of the policies of some of the people who are running."
"Do we reward that with the White House?" she asked to applause.
Physician Paul Y. Song, a health care activist and Sanders supporter, issued a crass attack on opponents, like Clinton, of more radical health care reform.
"Medicare-for-all will never happen if we continue to elect corporate Democratic whores who are beholden to big pharma and the private insurance industry instead of us," he said.
Song later apologized for the comment on Twitter, writing: "I am very sorry for using the term "whore" to refer to some in congress who are beholden to corporations and not us. It was insensitive."
The Clinton campaign did not immediately respond to a request for comment.