Union workers rallied Monday in front of the Picasso statue in Daley Plaza to denounce a lawsuit being heard right about then in the U.S. Supreme Court — a case they called an open-and-shut case of union busting.

“This court case was cynically designed to try and weaken the voices and power of working people,” said Kimberly Smith, a healthcare administrator and member of Service Employees International Union, Healthcare Illinois-Indiana, one of the organizers of the rally.

“In fact, destroying the union movement is what motivates [Gov. Bruce] Rauner — it’s all he thinks about before he goes to bed,” Smith told a cheering crowd of about 100.

The case, Janus v. AFSCME Council 31, involves an Illinois worker, Mark Janus, and what are called “fair share” fees.

Unions are allowed to collect those fees from workers who are not dues-paying members of the union. The fees help pay for collective bargaining and other work the union does that benefits all employees covered by the contract, whether they are dues-paying members or not.

Janus, however, disagrees with some of the political stances taken by his union, the American Federation of State, County and Municipal Employees. Janus and conservatives who are backing his lawsuit, argue that everything unions representing public employees do is political, including contract negotiations.

Labor leaders fear that not only would workers who don’t belong to a union stop paying fees, but that some union members might decide to stop paying dues if they could in essence get the union’s representation for free.

Rauner, an opponent of “fair share” fees, was in Washington to attend oral arguments in the case before the Supreme Court.

In Chicago, attendees at the rally handed out Proud Union Home signs for passersby to put in their windows or front yards.

“We will be Governor Rauner’s worst nightmare come election day on November 6,” Smith said.

SEIU-Healthcare and SEIU-Local 1, two of the unions who helped organize the rally, are part of a group of unions and other investors holding ownership stakes in the Chicago Sun-Times.

Kim Akins, a special education classroom assistant from Jackson Park who wore purple lipstick Monday — the main color in SEIU’s logo — thinks the case represents an existential threat to unions.

“We need our structure, we need our power, we need to be able to be a union so we can fight together,” she said.

Jeffrey Howard, who works in the main office of SEIU Local 73, said unions are not going to fade away just because that’s what wealthy political donors would prefer.

“I think it’s important that billionaires understand that unions are not going to go away,” said Howard, 53, who lives in Bronzeville. “We’re going to continue to represent workers and working families.”

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Contributing: AP