MUMBAI — Indian regulators have begun an informal inquiry into allegations that Wal-Mart Stores violated rules restricting foreign investment in the country’s fast-growing retailing industry.

The regulators are investigating an investment of nearly $100 million by Wal-Mart in an Indian company, Bharti Retail, which operates more than 200 supermarkets across India, at a time when India restricted foreign investments in retailing. The investment took the form of debt securities that paid no interest to Wal-Mart but could be converted into a 49 percent ownership stake in Bharti.

India long prohibited foreign equity investments in retail chains that sell more than one brand of products, known here as multibrand retail. It recently changed those rules to allow foreign companies to own up to 51 percent of such stores, but that change has faced stiff resistance from opposition political parties and even allies of the governing coalition.

Wal-Mart has long wanted to expand into India, where small, family-owned stores dominate a retail sales market worth about $500 billion annually. The company has a 50-50 venture with Bharti that operates 17 wholesale stores, and it provides logistics and management services to Bharti’s Easyday retail stores.