I run a large facility. People are parking in handicap spaces and I suspect they are not disabled. Can I ask for verification?

They must display a handicapped license plate or hanging card to park in a handicapped spot. No plate, no card, no park. A glearly handicapped person can still get a ticket for parking in a handicapped spot without a plate. Is you handicapped spot clearly marked with a handicapped sign? Got to have the sign Handicap Parking - Adaptive Access

If you have parking spaces marked as handicapped-reserved, anyone who parks in those spaces must display an appropriate tag. If there are people parking in handicaped reserved spots that do not have the appropriate tags, you can ask them to move, or ask local police to ticket their cars. You do not need to get involved in having the individuals "prove" their disability to you (unless you're a doctor you aren't qualified to make that judgment anyways) - you only need to check whether they display the tag, or move the car.

Keep in mind that you are not the parking police. You are required by law to provide a certain number of handicapped spots but have no authority to enforce any law. You might distribute a memo to all employees are a reminder but if they keep parking there without the porper license just call the police. They usually like the $250 tickets.

No handicapped placard no park in handicapped space. As far as proving their handicap to you the employer, you don't have to ask. You just need to see their placard properly displayed in their windshield of their car.

A reminder memo needs to be sent out or better yet, you could affix your reminder memo to the offender's windshield reminding them not to park where they are not supposed to park. All the other employees will see your "reminder memo" firmly affixed to the offender's car and get the message in a hurry.