Is it legal for my employer to take 50% of my gratuity?

Question Details:

I work in the catering business for a medium sized company. We charge customer labor as a line item on their invoice and also an automatic gratuity. We charge $40 per hour for each server and I only make $15 per hour. They are obviously making money on our hour and the food. Is it legal for them to take our tips as well? The client thinks that we are getting taken care of and are receiving the gratuity listed on their bill. Wouldn't this be like a server working in a restaurant having to give half of all their tips to the house? I don't feel like it's fair. In MN. Important Notice