In most states you can limit carry over vacation. Federal law does not speak to this, it is a state law. I suggest you contact the Nebraska Department of Labor for your answer.
50 Employment Laws in 50 States (click here if you are an HR Laws subscriber or click here if you would like to learn more about the book) says this about "use it or lose it" policies in Nebraska: “Use it or lose it” policy: No laws prohibit such policies, and “use it or lose it” policies are generally deemed to be merely a cap on the amount of benefit that may be accrued, provided that employees are given clear and fair advance notice and that employees are given ample opportunity to use the paid leave prior to its expiration.
Comments
Hope this helps!
Celeste