A giant Indian outsourcing company with thousands of employees in the United States is facing an expanding federal investigation prompted by claims from an American whistle-blower that it misused short-term visitors’ visas to bring in low-cost workers from India.

Accusations that the company, Infosys Technologies, repeatedly violated the terms of business visitor visas were first raised in a lawsuit filed in February in Alabama by Jack Palmer, an Infosys project manager. Aside from Mr. Palmer, at least two other Infosys managers in the United States have submitted internal whistle-blower reports pointing to Indians on business visitor visas who were performing longer-term work not authorized under those visas, according to internal documents and current Infosys managers.

In May, Infosys acknowledged that it had received a subpoena from a federal grand jury in Texas seeking information about the company’s use of the visitor documents, known as B-1 visas, which are easier to obtain. This month, N. R. Narayana Murthy, an Infosys founder, expressed his concern about that investigation at a board meeting in Bangalore, India, in his final address before he retired as company chairman.

“As I leave the board, I feel sad” about the subpoena, he said. “The issue will be decided on its merits in due course,” said Mr. Murthy, who is something of a legend in global business for building the company over three decades from a $250 investment into an outsourcing powerhouse with $6 billion in revenues.