"Unfair" is the plain, common, usual word. Why do you want any alternative? "Biased," "arbitrary," and "partial" are synonyms for "unfair."

inequitable,oppressive, wrongful

It's interesting. I don't know if this varies from language to language. In English it's considered quite normal to create negatives with the prefixes "un-" and "non-" and these are often the most-commonly-used words. By the way, the words "unbiased" and "impartial" exist--and, of course, mean "fair!"

inequitable discriminatory

Deceitful