"I'm highly confident" about the outcome, Rauner said in December. "With Gorsuch at the Supreme Court, we believe we will prevail."
Union leaders see the case as a well-funded political attack on public employees. "This is about power. They are attacking us because we fight for a better life for working people," said Randi Weingarten, president of the American Federation of Teachers. They say they are reasonably confident members will continue to pay their dues, even if they are no longer required to do so.
Beyond politics, however, the legal question before the court is whether requiring public employees to pay a fee to a union to cover the cost of collective bargaining amounts to "compelled speech" that violates the First Amendment.
For most of American history, government employees did not have protected rights under the Constitution. The justices often cite Oliver Wendell Holmes' comment in 1892 that a policeman "may have a constitutional right to talk politics, but he has no constitutional right to be policeman."
It was not until the late 1960s when the court first held that public employees had free speech rights, but only when they were speaking as citizens on a matter of public concern. The justices ruled unanimously in 1968 for Marvin Pickering, an Illinois schoolteacher who was fired for sending a letter to the editor of a local newspaper that was critical of the school board.
But the court has insisted public employees do not have rights to speak out about problems in the workplace. In 2006, the court said the First Amendment does not generally protect government whistleblowers from being punished or demoted. In that case, Garcetti v. Ceballos, the court ruled 5-4 against a Los Angeles county lawyer who said he was demoted for having revealed a police officer may have supplied false information in a search warrant. The court's conservatives sided with their employer. "A government entity has broader discretion to restrict speech when it acts in its role as employer," and a public employee "must accept certain limitations on his or her freedom," wrote Justice Anthony M. Kennedy.
Harvard law professor Charles Fried, the U.S. solicitor general under President Ronald Reagan, filed a brief in the union case questioning how the court could say the First Amendment protects public employees from paying a union fee, but not for speaking out about problems in an agency.
Meanwhile, several prominent First Amendment scholars with conservative credentials filed briefs questioning the premise that union fees involve speech.
"We think this is not compelled speech. It's a compelled payment of money," said UCLA law professor Eugene Volokh. He noted lawyers, doctors and other licensed professionals are required by state laws to pay fees for continuing education classes, including on topics some may oppose.
The Supreme Court upheld mandatory bar dues for lawyers in 1990, relying on the Abood decision. And in 2000, the court rejected a free speech challenge to the required student fees at state universities. Conservative students at the University of Wisconsin had sued, contending they should not be forced to subsidize left-leaning speakers and student groups.