Two US Congressmen have launched an investigation into allegations of bribery at Wal-Mart's Mexican operations, after reports emerged that it covered up some US$24m in payoffs to clear the way for store openings.

Wal-Mart's Mexican operations have come under increasing scrutiny after the New York Times reported that investigators appointed by the retailer found a paper trail of "hundreds of suspect payments totalling more than $24m" used to bribe Mexican officials to speed up store openings.

The report said the investigators also found documents showing that Wal-Mart de Mexico's top executives not only knew about the payments but had taken steps to conceal them from Wal-Mart's headquarters in Bentonville, Arkansas.

In a letter to the retailer, Elijah Cummings, from the House Oversight and Government Reform Committee, and Henry Waxman, from the House Energy and Commerce Committee, said they were launching an investigation into the allegations.

The congressmen said the report "raises serious questions about potential violations of United States law, including the Foreign Corrupt Practices Act".

They added that it "also raises significant questions about the actions of top company officials in the United States who reportedly tried to disregard substantial evidence of abuse".

They are seeking an investigation and a meeting in-person with company officials no later than 27 April.