Elon Musk said Apple Inc.
AAPL,
-2.63%
is threatening to remove Twitter Inc. from its App Store and criticized the tech giant for what he called censorship. He also said the iPhone-maker has withdrawn most of its advertising spending from the social-media company.

In a series of tweets Monday, Mr. Musk asked if Apple supports free speech and posted a poll asking users whether Apple should publish all censorship actions it has taken that affect its customers. Mr. Musk also asked Apple Chief Executive Tim Cook in a tweet, “What’s going on.”