The Fair Trade Commission is investigating whether clauses in contracts for liquefied natural gas that restrict buyers from reselling the fuel violate the competition laws of the world's largest user of the super-chilled gas, according to people with knowledge of the matter.

The investigation is in an early stage and the FTC has held hearings with energy companies, said the people, who asked not to be identified because the information is private. The commission's findings may be announced as early as this year, two of the people said.

Removing the restrictions would accelerate the shift by Japanese LNG buyers from traditional importers to international sellers, and highlights a power shift away from producers amid a global glut. The investigation follows a European Commission decision in October 2004 that the clauses restricted competition.