Bernie Sanders spoke at a rally in New York City on Monday, criticizing Verizon for not treating its union workers well. Twitter/CWA Sen. Bernie Sanders (I-Vermont) slammed Verizon on Monday during a surprise stop at a protest organized by a union that's bargaining with the company for a new contract.

Appearing at a picket line hosted by the Communications Workers of America in Times Square on Monday, Sanders criticized Verizon for not treating its union workers well, saying the company is a "metaphor" for corporate greed taking place nationwide.

"Middle class in this country is disappearing, and what Verizon is doing to their workers is exactly what has got to be fought if we're going to rebuilt the American middle class," Sanders said to loud cheers from the union audience.

"All over this country, Verizon is a metaphor," he said. "You've got corporate America making huge profits, their CEOs getting huge compensation packages. And then with all of their money, what they do is hire lawyers in order to make it harder for workers to survive in this country."

Verizon and the CWA have been at an impasse in the renegotiation of contracts for union workers, of which Verizon employs several thousand.

The organization has mounted an intense campaign against Verizon over a Brooklyn employee named Bianca Cunningham, who has said she was fired after organizing stores in Brooklyn. (Verizon spokesman Rich Young said the company has "not targeted Bianca Cunningham or any other employee for their union-related activities.")

In his speech on Monday, Sanders weaved the themes of his campaign into the speech, calling on the company to provide favorable terms and benefits for union workers. He also requested that Cunningham get her job back.

"It is not acceptable to me that when workers form a union and negotiate for an entire year they can't yet get a contract. That's not what democracy is supposed to be about. That's what rotten labor law is about, and we're going to change that," Sanders said.

Though his remarks lasted only 10 minutes or so, the senator became fairly specific in his criticism of Verizon. He said the company should create more broadband, which the CWA has alleged the company was supposed to do.

"I think Verizon needs to hear from the American people. We want them to create more broadband. We want them to pay their workers a decent wage. We want them to sit down and negotiate a decent contract," he said.

In a statement, Young, the Verizon spokesman, called the rally a "stunt":

These PR stunts do nothing to help advance the bargaining process. Verizon remains ready to hold serious discussions and engage in meaningful negotiations that will result is a fair and balanced agreement. We truly hope union leaders are soon committed to doing the same.

As The Huffington Post's Dave Jamieson pointed out, it's exceedingly rare for a presidential candidate to join a picket line.

Before the first Democratic debate earlier this month, former Secretary of State Hillary Clinton joined the Culinary Workers Union in a rally outside of the Trump Hotel in Las Vegas.

Brett LoGiurato contributed reporting.