It is a negotiation not a fairness discussion (even though fairness is part of the negotiation arguments). I asked about it in my current job before accepting the offer and was able to successfully negotiate it. In your situation, it seems that the only way is to look for a new job.

Anyway, the way I negotiated was very simple. Basically a version of ”I understand that this is a good salary relative to my local market, but I am not even looking for jobs in my local market. I am comparing your offer to offers from other US-based companies that I received for remote work.”

That was it. The part of other offers was true of course (even if for companies that I wasn’t too excited to work for). No need to even reply to their arguments of “company policy”, “cost of living”, whatever. I only have to state my point of view.

There is also the topic of me not receiving benefits like health care and 401k and other stuff that American employees get. I didn’t use this argument (didn’t occur to me), but I have the impression that this was considered in their calculation in how much to raise their offer.