Toshiba and Hitachi have joined Sony in an antitrust investigation. The US Department of Justice will probe the companies' optical disc drive businesses, Toshiba Samsung Storage Technology and Hitachi-LG Data Storage. Sony's Optiarc America was subpoenaed yesterday.

None of the companies have disclosed what products are being investigated, but rumors suggest that it may be related to the high cost of Blu-ray. Combined, the companies account for some 60% of the optical drive market, so it wouldn't be surprising if they've been involved in some form of price-fixing and bid-rigging – especially considering AT&T's recent allegations of an LCD conspiracy.

Sony, Toshiba and Hitachi have all agreed to comply with the investigation, and it could be a while before specific details of the case emerge.