The problem is that the GPL states:

You may not impose any further restrictions on the recipients’ exercise of the rights granted herein.

Red Hat are arguing that they are free to punish customers from exercising their rights under the GPL, and that punishment does not constitute a “restriction”, even though its done specifically to discourage people from exercising those rights. Whether Red Hat have found a loophole is something for the courts to decide, but it’s clearly against the intention and spirit of the GPL.

This is something for the courts to resolve, but it seems to me that there’s a good argument to say that threats of future punishment (explicit or implied) would constitute a “further restriction” under the GPL.

It doesn’t seem likely that would be allowed, as it would arguably constitute a restriction on distribution, which the GPL explicitly forbids.