I don't know that I'd agree with the negative definitions that you've included, since discrimination really only means to choose between options. The real question is whether or not your situation represents improper or illegal discrimination. I'd suggest that you discuss this with your union representative, or someone at a higher level in the union if your local rep. had no involvement in the negotiations over your new contract, and find out what the understanding was during the negotiations of the term "domestic partner". If the contract, or the health insurance program if that is a separate agreement, spells out that this covers same-sex couples only, I think that you're probably dead in the water.