The Japan unit of U.S. pharmaceutical giant Johnson & Johnson and a Tokyo-based firm selling medical products were searched by the country's antitrust watchdog over potential violations of the antimonopoly law, sources close to the matter said Tuesday.

The Japan Fair Trade Commission suspects Johnson & Johnson K.K. and ASP Japan of obstructing competitors' sales of cleaners and disinfectants for endoscopes.

ASP Japan said on its website that it was formerly under Johnson & Johnson until 2019 and specializes in infection prevention technology.

According to the sources, the companies allegedly required that only their disinfectants be used in endoscope cleaners that their trading partners produce. They are also believed to have created equipment maintenance contracts with hospitals that stipulate using their disinfectants.

The commission said it is looking into possible obstruction of trading and forced buying of tie-in products. Japan's antimonopoly law bans both practices.