I work for a nursing home doing 12 hour shifts. They only pay overtime for over 80 hours in 2 weeks. Is this legal?

A nursing care facility may elect, if the employee or the employee's union agrees, to what is known as an "8 and 80 system" for calculating overtime.  In electing to use this system, the employer obligates itself to pay overtime (1.5 x the regular hourly rate) for each hour worked in excess of 8 in a day and 80 hours in a two week period.  Google the term "8 and 80 system" and see if you can find an explanation that describes the specifics of your situation. For example your question does not specify whether you are being paid overtime for your daily overtime hours (in excess of 8) when your total hours for the two week period do not exceed 80.