Several Points
The Sultan is the absolute ruler of Brunei. He personally is responsible for the institution of sharia law in that country. Yes, other repressive regimes are guilty of gross crimes against humanity yet this is a case where loathsome policy can be tied directly to one man.
Does it matter that it is reported that the initial call for the boycott, at least in LA, was issued by a union? Not in my book. The insinuation here is that the union is disingenuous because their real beef is the non-union status of the BHH and anti-union practices at Hotel Bel-Air. Then, too, there is the suggestion that the union is two-faced because it doesn't really care about LGBT rights because unions in general are bigoted. This is anti-union rhetoric and, yes, some unions have engaged in blatant racism, sexism and bias in the past. The labor movement has its historical demons but that should not invalidate the many gains and protections it has won for workers. Today the labor movement sides firmly with civil rights for all societal sectors.
I will respect the boycott although I do not think boycotts are effective in making positive change, especially in this case against one of the world's richest people. He is not likely to feel or care about the financial impact. It could be hoped that public shaming and execrable PR might have an effect but I doubt it because this is the man who personally made sharia the law of his land.
If the boycott is at all effective, it would be good if those supporting or respecting it were to establish a fund to assist in the living costs of workers who lose jobs as a result.