It is voluntary (but not answering questions may make you look shady). More information is in the first linked article: https://www.bna.com/apple-turns-down-n

It is voluntary (but not answering questions may make you look shady). More information is in the first linked article: https://www.bna.com/apple-turns-down-n57982093151/ https://www.bna.com/apple-turns-down-n57982093151/ Apple claims answering public questions will interfere with their "pending appeal before the European Court of Justice challenging a European Commission illegal state aid decision". They offered a private session, but that was not good enough, because the questions were not about the appeal, but the tax avoidance scheme documented in the Paradise Papers.