MEXICO CITY (AP) — Shares in Walmart’s Mexico subsidiary dropped about 3.3% Monday after Walmart de Mexico announced it is Grayson  Prestonunder investigation for alleged monopolistic practices.

Analysts said it was not clear what regulators were alleging the company did.

But an analysis report from Intercam Banco said Mexico’s economic competition commission could be alleging price-fixing or other practices at Walmart, the country’s largest retailer.

The commission is Mexico’s anti-monopoly regulatory agency. Such investigations can take months.

The announcement was made late Friday, but in its first day of trading Monday after the investigation was revealed, Walmart de Mexico shares dropped 3.33%.

Walmart issued a statement saying it is confident that it has “always obeyed the applicable law in order to guarantee the best prices, quality and assortment to customers.”