I'm not sure how the wellness program would lead to discrimination... unless you plan to blatantly discriminate...
I think to answer this question we would need to know more about what you term a "wellness" program... because it includes everything from things to help people quit smoking and losing weight to merely paying for a health membership...
Ultimately you shouldn't run into discrimination issues unless they aren't offered for everybody or you somehow tie them to earnings in any way. Most people skirt this issue by declaring the wellness program optional and as an additional benefit of employment, not as a substitute for actual benefits.
Cheers!
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In life, there is a lot less that could get better and a lot more that could get worse.
MBA Fin/MBS HR
My views only!