The Commission, which sent letters to several companies involved in the development of both technologies, would not specify which companies had been contacted.
HD-DVD was created by Toshiba Corp, while Blu-ray Disc was developed by a Sony-led consortium, which includes Philips, Samsung and Sharp Corporation.
"We have sent a letter earlier this month to the makers of HD-DVD and Blu-ray to request information about licensing," a Commission spokesman said.
The spokesman declined to give further information.
Sony confirmed that it had received requests for information and that it is cooperating fully.
"There are no indications of any complaint, nor of any antitrust concerns on the part of the Commission or anyone else," a Sony spokesman said.
According to a Reuters report, the inquiry, which is not a formal investigation, will address whether the licensing terms of the DVD formats break any European Union competition rules.
The owners of the DVD formats license their technologies both to companies that manufacture hardware as well as producers of DVD titles, an arrangement that seems to be giving rise to antitrust concerns.
HD-DVD came to market in the U.S. in April. The format enjoys support from Intel and Microsoft as well as the exclusive backing of Universal.
Blu-ray, which was released in the U.S. in June, claims support from 20th Century Fox and MGM.
Blu-ray is expected to launch in Europe in early 2007. HD-DVD appears to be shooting for a European launch late this year.
In the meantime, both formats have failed to capture widespread market share in the U.S., with few consumers adopting either format.