"The U.S. Justice Department has reached out to app developers as part of its investigation into Apple Inc, one of the four big tech companies being probed for alleged anti-competitive behavior, according one of the developers and another person familiar with the investigation."

Exclusive: iPhone app makers questioned in U.S. antitrust probe of Apple - sources - Reuters https://www.reuters.com/article/us-tech-antitrust-apple-exclusive-idUSKBN1ZY29M