The European Commission has opened a formal investigation into Corning to determine whether it has broken antitrust rules with its dominant Gorilla Glass product. Corning’s Alkali-aluminosilicate glass is used to protect most of the top phones and tablets, with both Samsung and Apple using it extensively across their range of devices. The EU is concerned that Corning has used a variety of exclusivity contracts to exclude rival glass makers from the phone market.

“It is very frustrating and costly experience to break a mobile phone screen. Therefore, strong competition in the production of the cover glass used to protect such devices is crucial to ensure low prices and high-quality glass,” says outgoing EU competition chief Margrethe Vestager. “We are investigating if Corning, a major producer of this special glass, may have tried to exclude rival glass producers, thereby depriving consumers from cheaper and more break-resistant glass.”

The Commission’s concerns are centered on the agreements with mobile device makers and companies that produce raw glass. The EU is looking into exclusive sourcing obligations that have required device makers to source “all of nearly all” of their glass from Corning, enabled rebates for exclusivity deals, and forced device makers to report on competitive offers and only accept them if Corning failed to price match.

If Corning is found guilty of breaching EU competition rules then it could face a fine, but the glass maker will also have the opportunity to address the Commission’s concerns with a set of commitments that can bring the antitrust investigation to an end.

Corning’s Gorilla Glass offers additional damage resistance for phone and tablet displays against scratches, bumps, and drops. It was once a major selling point for Apple’s iPhone devices, before Corning’s Alkali-aluminosilicate glass became a dominant feature in modern smartphones.