Companies seeking to take advantage of a shake-up in Australia's media ownership laws face antitrust action if they acquire control of too much content, such as sports and movies, the head of the country's competition watchdog has warned.

The government is this week expected to unveil its long-awaited paper on the relaxation of Australia's restrictive media ownership laws. The changes are predicted to spark a wave of merger and acquisition interest in the sector from overseas and domestic companies.