Working folks aren't a protected class but I will say that your ratings will take a hit if you keep denying bookings for no obvious reason.Have you had massive damage due to a work group staying? 

Even a request for last 6 months income was denied.

Quote from @Denis Ponder: I play basketball a few times per week, go for walks or cycle (Zwift on a smart trainer has been amazing!) 

@Kyle Pierrehumbert it's easy for all the commentors to tell you to deny these applicants.REALITY: many tourist-related businesses are having a hard time finding seasonal workers due to lack of affordable housing!

Is it legal for me the landlord to deny a rental application due to the applicant admitting they smoke?

NOPE denied.. 

I'm not going to deny someone their pet for a vacation, sometimes all they have is that pet.

You can continue the process but it will be denied.

The PM's I have talked to that have experience with them said that they have never had a claim denied. 

Even if you apeals are denied you can apeal to a higher level.