On the cusp of a U.S. Supreme Court showdown in a case being watched closely by workers' unions across the country, more than 1,000 people gathered in Philadelphia Saturday morning to rally in support of organized labor.

Mayor Kenney was among the officials at the "Working People's Day of Action," telling the crowd at Thomas Paine Plaza that he was a "proud supporter of unions."

"Whenever the rights of unions are threatened we need to fight back," Kenney said. "And we will."

Similar rallies were held in cities across the country, including Detroit, San Diego, and Columbus, Ohio.

The event came just days before the nation's high court is scheduled to hear oral arguments on whether public sector employees should be compelled to pay fees to unions even if they don't want to join them. The plaintiff in the case, Illinois resident Mark Janus, has argued that such fees — called "fair share" payments, which are generally less than member dues — violate his First Amendment rights because they force him to support organized labor.

Labor supporters have argued that the fees prevent nonmembers from enjoying the benefits of collective bargaining without having to pay. Eliminating the fees could also have a crippling financial impact on workers' unions across the country, which for years already have been battling decreasing membership rolls.

Last year the court was deadlocked, 4-4, when deciding the case, referred to as Janus v. AFSCME. President Trump has since appointed Justice Neil Gorsuch to the bench, widely considered a conservative and thus a threat to tip the scales toward an anti-union verdict.

Speakers and attendees at Saturday's rally — including labor leaders, union members, and clergy — regularly referenced the case, which has been considered one of the most consequential facing organized labor in decades.

Keenan Fields, 48, of Sharon Hill, a shop steward and member of United Food and Commercial Workers (UFCW) Local 1776, said organized workers "absolutely" felt worried about the Janus case and other potential legislation threatening unions.

"We just want a piece of the pie," he said. "Give us our piece and let us be happy."