Japanese regulators are considering taking action against Apple over possible anti-trust violations that may have helped it dominate the nation’s smartphone sales, government sources say.

In a recent report , Japan’s Fair Trade Commission (FTC) said that NTT Docomo, KDDI Corp and Softbank Group are all refusing to sell older surplus iPhone models to third-party retailers, thereby hobbling smaller competitors.

Apple was not named in that report, but two senior government sources told Reuters that regulators were focusing on Apple’s supply agreements with all three carriers.

Under those deals, surplus stock of older iPhones is kept out of the US market and sent to overseas markets, such as Hong Kong, according to industry sources.