I work as a contract employee at a federal government site located in Maryland. Our gov't employer is trying to force employees to work an 8 1/2 hour day with a 30 minute unpaid lunch break vice just an 8 hour day for those employees who work through lunch. Is this legal if there is not provision in our contract that affords for this requirement? All employees are over 18 and are exempt, salaried employees.

Barring a bona fide contract that says otherwise, it is absolutely legal for an employer to require you to take a lunch break.

Do you have a legal reference I could give my boss who I am doing this research for?

No, because laws don't say what individuals or employers are allowed to do, only what they are prohibited from doing. Since there are no laws that prohibit an employer from determining their employees' work schedules (including mandatory rest or meal breaks) the right is presumed. We can't point you to a law that doesn't exist.

Management has an absolute right to determine the hours of work. I presume you have employees that want to skip lunch and leave early? The tail doesn't wag the dog.