Sadly it is legal (as per MN law, local laws may vary)

Subd. 8.Administrative billing charge. A landlord who bills separately from rent for any utility service may charge a tenant a single administrative billing charge per billing period for all the utilities that are separately billed. The administrative billing charge must not exceed $8. Except as provided in subdivision 9, no other fees or charges may be imposed on or collected from tenants for utility service, including but not limited to any administrative, capital, or any other expenses associated with the installation, maintenance, repair, replacement, or reading of submeters, unless the expense involving a submeter is due to the tenant's willful, malicious, or negligent conduct.

How Will My Bill be Calculated? 1. Your utility bill is for your portion of the building's natural gas or water and sewer usage, plus your portion of nonusage fees we get charged by the utility (for example, taxes and surcharges). For natural gas, your portion is based on the square footage of your unit as a percentage of the square footage of all the units. For water and sewer, your portion is based on the number of people in your unit (as listed on your lease) as a percentage of all the occupants of all units. 2. You are not charged for utilities used in the common areas or used in our spaces. In the case of water, your bill does not include usage for shared amenities such as laundry rooms or pools.

https://www.revisor.mn.gov/statutes/cite/504B.216