Regulators are considering taking action against Apple Inc. over possible antitrust violations that may have helped it dominate Japan¡¯s smartphone sales, government sources said, a move that could damage the company¡¯s profit margins in one of its most profitable markets.

In a report published last month, the Fair Trade Commission said NTT Docomo, KDDI Corp. and SoftBank Group were 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 said regulators were also focusing on Apple¡¯s supply agreements with all three carriers.