The U.S. has joined German and Russian authorities in investigating whether Hewlett-Packard Co. executives paid millions of dollars in bribes to Russian officials to win a contract in Russia, according to people familiar with the matter.

The U.S. Justice Department and Securities and Exchange Commission are investigating whether H-P committed any violations of the Foreign Corrupt Practices Act, these people said, as part of a widening probe into the company's activities. The law bars American companies from bribing foreign-government...