It’s not different from race in that regard.

The basis of the legal challenge is on the law saying you cannot discriminate against protected classes, race, disability, gender, etc.

There isn’t a specific rule preventing affirmative action, taking steps to mitigate prior discrimination, from happening, but in practice, there is often enough an argument that can be used, that helping a disadvantaged group is still discriminating against another group.

While I support UBI and affirmative action in general, there’s a very real chance this will lose a court battle.