Am I allowed to refuse a larger family than I think appropriate?

[Johann Jells]

I know family status is a protected class, but must I rent to an applicant that while they don't violate the state occupancy limits, seems too much by my judgement? 

I have a 450 ft 1BR that a family of 3 is inquiring about. That seems too small even though the state allows occupancy of non-bedroom space. Of course I wouldn't be kicking out a couple that had a baby while in residence, but I'd expect them to move soon, and they usually do, even from my small 2BRs. 

I've actually had inquiries of 4 adults for these units! I'd rather lose a month than rent to people so close to the edge. I stated in the ad I required 3x gross rent in income, and had an inquiry that wasn't even 1.8x!  I Don't know what they're thinking never mind how they manage.