Apple so far has avoided the worst outcome in its U.S. legal battle with Epic Games, but its antitrust woes remain. In the last several months the U.S. Department of Justice has accelerated its two-year-old antitrust probe of the iPhone maker, according to two people with knowledge of the investigation, increasing the likelihood of a lawsuit.

Since summer, there has been a flurry of activity on the investigation as DOJ lawyers have asked Apple and its customers and competitors questions about how the company maintains its strict control over the iPhone, the people said. That includes a new round of subpoenas sent to Apple’s business partners over the summer, according to people familiar with the matter.