Yes and they frequently are. Domestic partners, which may be of either same or mixed genders, are often treated differently than legally married couples, particularly in the legal context. Right off the bat, there is an entirely different set of vocabulary words that are used in connection with their relationship.
If they are registered, then they often are granted only a subset of legal rights and benefits of marriage. Although opposite-sex couples have consciously chosen not to marry, same-sex couples might have settled for domestic partnership because it was the only option available.
If your question is whether it is legal to discriminate against domestic partners (i.e., treating them differently than legally married couples), then the answer in many jurisdictions is yes. In many states, the law itself draws a distinction between married couples and domestic partners. In some places, such as California, Oregon, Nevada and, for the time being, Washington state, state-registered domestic partners are entitled to be treated the same as legally married couples.
Being discriminated against for your religion
right to be treated equally and not discriminated against
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They discriminated in that punishments for crimes were not the same for the Chinese.
Cesar Chavez was discriminated against for several reasons. It would be almost impossible for a Latino farm worker not to have been discriminated against, especially during his time.
Domestic assault in Tennessee is an assault against a victim. The state prohibits the abuse of current or former family members or romantic partners.
They discriminated in that punishments for crimes were not the same for the Chinese.
If you are not registered as domestic partners, then you are not legally recognized as domestic partners. However, in jurisdictions where there is no government registry of domestic partnerships available, many companies offer domestic partner benefits based upon a notarized affidavit of domestic partnership submitted to the company, with no requirement for government registration.
Being discriminated against for your religion
They discriminated because punishments for crimes were unequal.
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Everyone can be discriminated against. Humans tend to be frightened by differences, so those who are different or those who go against social norms of a culture tend to be discriminated against. Common discriminations include discrimination against the minority race, women in certain cultures, or homosexuals.