The currently popular Bee Token has cancelled their Bounty program stating:
"GUYS OUR BOUNTY PROGRAM IS NOW OFFICIALLY CLOSED, DUE TO NEW REGULATIONS WE HAVE HAD TO IMMEDIATELY CEASE OUR BOUNTY. AGAIN, THIS HAS NOTHING TO DO WITH US OR HOW WE RUN OUR BUSINESS AT ALL, BUT IS IN RESPONSE TO RECENT SEC COMMENTS. THANK YOU ALL FOR YOUR RECNT PARTICIPATION!!"
They didn't provide much more detail related specifically to The Bee Token but include an article by Andrew J. Chapin:
https://hackernoon.com/rest-in-peace-ico-bounty-programs-fc1e1e04e867
Andrew says:
"Participants were happy to receive free token, ICO project managers loved the free (organic-ish) marketing, and everybody was happy. Except for the United States Securities and Exchange Commission (SEC). Now, citing the all-mighty Howey Test, the SEC is pursuing American ICO operators who offer a bounty program."
In his article, Andrew includes video/blog bounties as well as airdrops. On the other hand, his argument is based on the fact that promoted coins should qualify as Securities due to the Howey test.