Is it legal for your employer to request you turn on your phone GPS during work hours to track you?

Yes it is. It is not uncommon for employers to provide employees with cell phones in order that they be able to perform their work more efficiently. However, since most of these products have some kind of GPS tracking system located within them, an employer can also use them to locate their employee and know where they are when the employee is on the clock and getting paid.
That having been said, with an incease in telecommuting and employees taking their work home with them, is there a point at which employers must refrain from tracking their employees? The fact is that many employees that are provided with phones keep them turned on at all times, even if they are not necessarily performing work-related duties. Many employers provide these phones so that employees are able to be contacted at any time. yet, does this mean that an employer should be able to track employees at any time? NY courts have taken the stand that at least as to public sector employees, they can only be tracked using GPS on their cell phone if the employee is engaged in a work-related duty during business hours.
Note If an employee has consented in writing to such tracking, that will also control their rights in such a situation.