The actual text of the Constitution is the final and absolute yardstick all laws are measured against. When the Supreme Court considers the constitutionality of any law it must measure the law against the original text of the constitution and its plain meaning when it was written.
Notice of working hours/changes. Your employer must give you reasonable notice of any changes to your working hours, such as cancelling your shifts. They may request last minute changes (such as ringing you that morning to say that they do not require you to work) and you can choose to agree to this change.
The U.S. Department of Labor's regulations for determining what must be counted as hours worked are found in Part 785 of the wage and hour regulations, Title 29 of the Code of Federal Regulations. For the majority of non-exempt employees, overtime will be an issue if the hours worked exceed 40 in a seven-day workweek. In general, an employer must pay employees for all hours in which they are suffered or permitted to work. Only hours actually worked in excess of 40 in a seven-day workweek are counted toward overtime pay; paid leave hours and paid holiday hours do not count toward overtime pay.