By Mike Scarcella

June 3 (Reuters) - Hotel giant Marriott MAR.O has persuaded a U.S. appeals court to reverse a ruling that allowed tens of millions of guests to sue together as a class over a 2018 cybersecurity breach that exposed a reservation database at its affiliate Starwood.

The Richmond, Virginia-based 4th U.S. Circuit Court of Appeals ruled on Tuesday that the hotel's guest contracts included a valid provision waiving class action claims, “and so precludes certification of all classes against Marriott.”

Marriott in a statement said it welcomed the court’s ruling. Attorneys for the plaintiffs had no immediate comment.

The decision marked the latest development in the closely watched, long-running litigation over the Starwood cyber breach.

Hackers in 2014 first accessed names, birth dates and other information, including payment card data in some instances, court records show, before the scheme was detected in 2018. Marriott purchased Starwood in 2016.

The proposed class action accused Marriott of violating consumer protection and other laws by failing to provide adequate data protection security. The plaintiffs said guests would have paid less for rooms if they'd known about alleged lax of data security.

The guests' contracts said disputes would be handled “individually without any class action,” according to court records.

A federal trial judge in Maryland found that Marriott’s participation in consolidated legal proceedings showed that it had given up its right to enforce the provision against class actions.

The appeals court disagreed, ruling that Marriott’s participation in the multidistrict proceeding did not deprive the company of relying on a contractual class-action waiver defense.

The U.S. Chamber of Commerce filed a brief backing Marriott in its appeal in the 4th Circuit.

The case is Maldini v. Marriott International Inc, 4th U.S. Circuit Court of Appeals, No. 24-1064.

For plaintiffs: Samuel Issacharoff of New York University School of Law; Amy Keller of DiCello Levitt; James Pizzirusso of Hausfeld; and Andrew Friedman of Cohen Milstein

For defendant: Lindsay Harrison and Matthew Hellman of Jenner & Block; Daniel Warren and Gilbert Keteltas of Baker & Hostetler

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(Reporting by Mike Scarcella)