"Wal-Mart has never lobbied on (the Foreign Corrupt Practices Act)," says spokesman David Tovar. "Simply because Wal-Mart is a member of an organization does not mean we agree with every position they take."

The U.S. Chamber of Commerce and Retail Industry Leaders Association (RILA) received letters Wednesday from Reps. Elijah Cummings, D-Md., and Henry Waxman, D-Calif., asking for information and documents related to Wal-Mart's efforts to lobby for changes to the Foreign Corrupt Practices Act.

• STORY: Anti-Wal-Mart groups use bribery charges to their benefit

• STORY: Bribe report puts focus on Mexico's 'gestores'

Top Wal-Mart executives serve on the boards of both organizations, which have lobbied against the act.

In a letter sent to the Securities and Exchange Commission and the Justice Department in February, RILA and the Chamber were among the groups expressing concerns about portions of the law, including inadequate definitions of "foreign official."

They added that confusion about when the law applies has had a "chilling effect on legitimate business activity."

Now, Cummings and Waxman are particularly concerned about whether Wal-Mart was involved in lobbying against the law at the same time top executives were aware of possibly having violated it, Cummings says.

"If that is the case, we want to make sure that we put in whatever barriers are needed to make sure that an effort like that is not effective," he says.

VIDEO: Wall Street analyst says bribery scandal won't hurt Wal-Mart in the long-term.

Wal-Mart allegedly spent more than $24 million bribing Mexico officials to get construction permits to help expand its reach in what's now its largest foreign subsidiary, the New York Times reported on Sunday.

The case also involve multiple instances in which Walmart de Mexico executives allegedly concealed the bribes from the company's U.S. headquarters.

Once the bribes were brought to the attention of U.S. executives, a preliminary investigation that confirmed possible illegal activity was shut down, against the recommendation of Wal-Mart's lead investigator, a former FBI agent, the Times said.

The committee now overseeing Wal-Mart's own investigation into the allegations "is comprised entirely of independent directors," Tovar says, adding that they have told Wal-Mart "to use whatever resources necessary to conduct an independent investigation."

Wal-Mart stock fell almost 5% Monday following the allegations over the weekend. Wednesday, it finished down 41 cents at $57.36.