According to CBS MoneyWatch, as long as an employee is paid by the hour for work done, an employee can send that person home early without pay. An employer cannot dock the pay of an exempt employee if that employee is at work and ready and willing to work.
For nonexempt employees, the failure to work means a lack of pay. In some industries it is not uncommon to be sent home from work if things are too slow to warrant paying additional help. While it can be annoying to travel a long distance to work only to be sent home due to lack of work, there is little an employee can do but try to make up the hours another time.