BRUSSELS (AP) — European Union regulators have launched an investigation into flight ticket distribution services on concerns that their agreements with airlines might result in more expensive plane tickets.

The EU's executive Commission said Friday that it has opened an antitrust investigation into Amadeus and Sabre, two major "global distribution systems" for airline tickets.

The Commission is examining whether their contracts may restrict airlines and travel agents from using other suppliers.

EU Competition Commissioner Margrethe Vestager said she's concerned any possible restrictions "could create carriers to innovation" and push up distribution costs for airlines, "ultimately raising ticket prices for travelers."

Amadeus of Spain and Sabre, a U.S. company, provide flight booking systems and reservation management software.

The Commission said the opening of a formal investigation "does not prejudge its outcome."