Senate Majority Leader Bill Frist (R-Tenn.) has been subpoenaed to turn over personal records and documents as federal authorities step up a probe of his July sales of HCA Inc. stock, according to sources familiar with the investigation.

The Securities and Exchange Commission issued the subpoena within the past two weeks, after initial reports that Frist, the Senate's top Republican official, was under scrutiny by the agency and the Justice Department for possible violations of insider trading laws.

Frist aides previously said he had been contacted by regulators but did not mention that the lawmaker had received a formal request for documents. The sources, who spoke on condition of anonymity because of the investigation, said Frist is expected to testify under oath about what he knew about the company's health in the weeks before he sold stock. Frist has told reporters that he did nothing wrong and that he directed the sale to eliminate potential conflicts as he considered a 2008 presidential bid.