The answer to this question is a little complicated: First, you need to know that this issue is covered by two laws: the federal Fair Labor Standards Act (FLSA) and New Jersey's Minimum Wage Act. Traditionally, the FLSA provides that your commute time is not considered compensable work. So time spent drivng from your home to your office or from your home to your first work site is not work time and is not counted as hours worked for the purposes of determining minimum wage or overtime. So the change proposed by your employer, probably would be legal under the FLSA.
Generally, like most states, New Jersey's state minimum wage law has been interpreted in accordance with the federal law. However, this is not required and it is possible that the state could take a different position on this particular issue. For example, Washington State's supreme court ruled in a similar case that where employees were driving company vehicles and were held accountable for driving those vehicles in accordance with their employer's policies and instructions, the commute time in the company vehicle was work time and was compensable under the state wage law. To my knowledge, there has not been a ruling by a New Jersey court on this issue.
For further information regarding this issue, you can always contact the New Jersey State Department of Labor and Workforce Development, Division of Wage and Hour Compliance. Here's a link to their site: