(Reuters) - Wal-Mart Stores Inc WMT.N must face a class-action lawsuit accusing the world's largest retailer of defrauding shareholders by concealing suspected bribery to help it expand faster in Mexico, a U.S. judge said.

A general view shows a Wal-Mart store in Monterrey, Mexico, August 10, 2016. REUTERS/Daniel Becerril

In a decision on Tuesday, U.S. District Judge Susan Hickey in Fayetteville, Arkansas rejected Wal-Mart’s contention that a Michigan pension fund had no standing to lead the case because it had not suffered losses on the retailer’s stock.

The decision means shareholders can sue Wal-Mart and former Chief Executive Mike Duke as a group over the alleged cover-up of bribery at Wal-Mart de Mexico. This could lead to a larger payout at lower cost than if individual lawsuits were required.

Class certification “would enhance judicial economy and efficiency,” given that many shareholders had small claims, and “concentrating the claims in defendants’ home forum with uniform decisions is desirable,” Hickey wrote.

Wal-Mart spokesman Randy Hargrove said the Bentonville, Arkansas-based retailer believes a class action is “not appropriate,” and may appeal the certification decision.

The market value of Wal-Mart fell by roughly $17 billion over three days in April 2012, after The New York Times published a Pulitzer Prize-winning report saying the retailer paid bribes to Mexican officials for years to speed up store openings.

Shareholders said Wal-Mart knew about the scheme as early as 2005, and downplayed it even after learning about the Times’ investigation.

Wal-Mart had argued that a widely-accepted accounting method prevented the lead plaintiff City of Pontiac General Employees’ Retirement System from showing it lost money on Wal-Mart stock.

But the judge said the pension fund could show losses under another widely-accepted accounting method, and that Wal-Mart failed to show why its preferred method was better.

The class period runs from Dec. 8, 2011 to April 20, 2012, Hickey said.

In July, a federal appeals court upheld Hickey’s April 2015 dismissal of shareholder claims against Duke, his predecessor Lee Scott, and Wal-Mart’ board. A Delaware state judge dismissed similar claims by other shareholders in May.

Robbins Geller Rudman & Dowd represents the Michigan pension fund. It did not immediately respond to requests for comment.

The case is City of Pontiac General Employees’ Retirement System v. Walmart Stores Inc et al, U.S. District Court, Western District of Arkansas, No. 12-05162.