A U.S. senator, in a rare move, joined business and employee rights advocates to weigh in on the next battle poised to be heard by the Supreme Court over the arbitration agreements proliferating in corporate America.

In his first friend-of-the-court brief as counsel of record, Sen. Sheldon Whitehouse, a Rhode Island Democrat, pressed for the right of independent contractors to litigate labor disputes in court in New Prime v. Oliveira. Oral arguments in the case are scheduled for Oct. 3. Groups, including the U.S. Chamber of Commerce and the National Employment Law Project, also have weighed in on the importance of the outcome of the case.

Whitehouse, a former U.S. attorney, has signed onto amicus briefs previously before the Supreme Court with fellow senators but never penned his own brief as counsel of record as a sitting senator. He argued the case has “no apparent business before the Supreme Court.”

“The Supreme Court going out of its way to grant this case suggests something else is going on beyond just 'calling balls and strikes,'” Whitehouse told the National Law Journal in an email. “As the Court keeps taking these cases and misinterpreting statutes to erode people's rights, its own institutional legitimacy suffers. Someone needs to make that known.”

The worker, Dominic Oliveira, was an independent contractor for the interstate trucking company New Prime Inc. and sued the company in a minimum wage dispute. His agreement with the company requires him to arbitrate workplace disputes. Oliveira, a long-haul truck driver, filed a class action and opposed arbitration. The U.S. Court of Appeals for the First Circuit sided with the driver, and the company appealed to the high court.

Whitehouse pointed to the string of pro-arbitration cases before the Supreme Court in recent years, including the recent the trio of cases— Epic Systems Corp. v. Lewis—that rubber-stamped class action waivers in mandatory arbitration agreements. Whitehouse said creating an imbalance of power for corporate interests was not what was intended when Congress passed the Federal Arbitration Act, the statute at the center of these disputes that gives power to such employment agreements.

Mandatory arbitration agreements have risen steadily over the decades to affect more than 55 percent of workers who sign employment contracts, according to data from the Economic Policy Institute.

“Any fair reading of the Supreme Court's 5-4 jurisprudence in the past decade shows a distinct pattern of the 'more powerful and wealthy' corporate interests gaining precedence over ordinary citizens,” Whitehouse wrote in his brief. He continued, “The recent string of 5-4 arbitration decisions has provided the 'more powerful and wealthy' interests an avenue to systematically deny ordinary individuals, such as those who are their employees or customers, access to juries of their peers when wronged.”

With Justice Anthony Kennedy's retirement, a new Trump-appointed justice will join the court. Judge Brett Kavanaugh, who has a history of siding with employers in disputes before the U.S. Court of Appeals for the D.C. Circuit, has been nominated to replace him. Kennedy typically sided with the conservatives on the bench in arbitration cases.

New Prime's lawyer Theodore Boutrous Jr., of Gibson, Dunn & Crutcher, wrote in a brief arguing for the court to hear the case that the outcome will be important for a wide swath of the economy to “restore the federal presumption in favor of arbitration nationwide.”

“Without this court's review, an entire sector of the economy, in a significant portion of the country, will be denied the benefits of arbitration and the protections of federal law, and the validity of millions of independent-contractor agreements will be cast into uncertainty,” Boutrous said.

Oliveira's lawyers at Public Justice said in July that the contract between them—for Oliveira to work for Prime hauling freight—is indisputably a transportation worker's agreement to perform work, and the Federal Arbitration Act should not apply.

“Prime's interpretation would also require this court to hold that employers can avoid the transportation-worker exemption simply by labeling—or mislabeling—their workers independent contractors, regardless of whether they actually are,” the attorneys wrote. “No federal law permits employers to circumvent its strictures by illegally misclassifying their workers. There is no reason the FAA should be any different.”

The case is set for argument on Oct. 3 at the U.S. Supreme Court. Other groups have filed amicus briefs, including the U.S. Chamber of Commerce, in support of New Prime.

“If the decision below is allowed to stand, however, untold thousands of arbitration agreements would be called into question,” Mayer Brown's Andrew Pincus wrote in the chamber's amicus brief.