Some users of communication service Slack have reported their accounts have been closed over visits to countries under US sanctions.
The move, which Slack says is to comply with US regulations, is believed to be affecting users who have visited nations including Iran and North Korea.
But many on social media say they were not warned in advance.
Some have said they had not visited the countries in recent years, and believe their bans were in error.
Cuba, Syria and Crimea are other countries and regions where Slack says its systems may not be used.
I was in Crimea this summer, and ran Slack there. I had a visa to visit Syria back in 1998, but ended up staying in Jordan several more days and didn’t get to Syria to see Palmyra. I regret not visiting Syria in 1998. This summer when I was planning visits to Turkey and Kazakhstan I did some looking at the map and thought about driving through Iran and Turkmenistan. I want to go to Iran before too long. I don’t want US corporations to interfere with my ability to chat with people just because I visited countries the US government doesn’t like.