WASHINGTON – Top Democrats on two U.S. House committees are readying a report on their four-month investigation into allegations that Bentonville-based Wal-Mart Stores Inc. violated the Foreign Corrupt Practices Act.

Reps. Elijah Cummings, D-Md., and Henry Waxman, D-Calif., launched their investigation in April after a New York Times report raised serious questions about potential violations of the law as Wal-Mart sought to expand its operations in Mexico.

Cummings and Waxman sent a letter Tuesday to Wal-Mart CEO Michael Duke giving the company "a final opportunity to respond" before they publish the findings of their investigation.

"Although you have stated on multiple occasions that you intend to cooperate with our investigation, you have failed to provide the documents we requested, and you continue to deny us access to key witnesses," the Democrats wrote.

Waxman and Cummings have written Duke four times since April seeking information on allegations that top Wal-Mart executives covered up actions by company officials in Mexico that may have violated the Foreign Corrupt Practices Act.

Cummings is ranking member of the House Oversight and Government Reform Committee. Waxman is ranking member of the House Energy and Commerce Committee.

Rep. Darrell Issa, R-Calif., who chairs the Oversight panel, has not launched an official investigation of the alleged Wal-Mart bribery scandal.

Wal-Mart last year launched its own internal investigation into allegations of corruption at its Mexican subsidiary. It has since created a Global FCPA Compliance officer position to oversee five FCPA compliance directors based around the world – including one in Mexico.

The company has also met voluntarily with the U.S. Department of Justice and the Securities and Exchange Commission to discuss their official investigations.

A call to the company’s press office was not immediately returned Tuesday.