Federal law does not entitle you to a lunch break. Unless your state law dictates otherwise, your employer can require you to work through lunch without stopping to eat. What an employer cannot legally do, however, is give you an unpaid break, then require you to keep working when you're suppose to be off the clock.
The federal rules for hours and overtime are part of the Fair Labor Standards Act, or FLSA. There is no restriction on how many hours you can work in a day, or any requirement for breaks or lunch time. If your employer wants you to work 10 hour days with no break, it's legal -- but if that adds up to more than 40 hours, you're entitled to time-and-a-half pay for the overtime. If you do have a lunch break, it you must receive compensation for the break break unless it's at least 30 minutes long.
A number of states mandate more break time than federal law does. Some states require that if you work more than five or six hours, you receive a lunch break in the middle of the day. Other states give you a 10-minute rest break for every four hours you work. Vermont guarantees you reasonable time to eat lunch, but doesn't define how much time is reasonable or when the breaks have to fall.
Some employees are exempt from overtime, no matter how many hours they work. If you're paid on a salary basis, meaning you get a minimum amount regardless of how many hours you work, receive above a minimum level set by the government and perform managerial job duties, your employer can ask you to work through lunch and into the night six days a week without overtime. Some employers classify ordinary workers as exempt to get around wage-and-hour laws, so check the standards if your bosses try this.
If your employer doesn't grant you a lunch break required by your state's law or has you clock out for lunch while continuing to work, you can contact your state labor department to file a complaint. If your lunch work runs into overtime and you do not receive compensation for it, you can also contact the U.S. Department of Labor. Federal fines can run as high as $10,000. You're also entitled to back overtime pay if the case holds up in court.