I believe that few people would wish to defend the disgusting remarks made by this person. However, in regard to his position within the RMT union, he will under legislation have to be treated in the same manner as any other employed person in the UK in regard to disciplinary action being brought against him.
In the above, there will have to be a disciplinary inquiry and if then it is found there is a case to answer a full disciplinary hearing will be convened.
Should he at that hearing be found to be in breach of any RMT staff rules or procedures a disciplinary penalty will be handed down. Steve Hedley will then, of course, be entitled to an appeal hearing against that penalty.
As Hedley placed these outrageous statements on his personal Facebook page it may be difficult to sustain a charge of "bringing the union into disrepute" unless he has made reference to the RMT and his position within it on that Facebook page it in recent weeks.
However, as stated, that situation would apply to any employed person in similar circumstances.