They were told by their clearing house they aren't allowed to continue allowing $GME trades due to capital requirements, and they have to let customers unwind their positions at any time.
If they had stopped all trading of the security because their clearing house wouldnt agree to the deal, thats one thing. When they limited only one type of trading which had an asymmetric affect on the different groups trading this security, then it looks like market manipulation, sounds like market manipulation, walks like market manipulation
Links? 100% of what I've seen is clearing required more collateral. I haven't seen one reliable source saying a clearing house outright forbid trading GME.
They were told by their clearing house they aren't allowed to continue allowing $GME trades due to capital requirements, and they have to let customers unwind their positions at any time.