Reading some of these responses amazes me as to what dispatchers allow administration / management to get away with..
Here is the issues... Keep in mind, your employment is a labor contract of sorts - EVEN IF IT'S NOT WRITTEN DOWN AS SUCH.
Additionally, the U.S. Supreme court has ruled that your job -is- one's personal property and cannot be arbitrarily seized. EG - firing without cause is illegal.
With this in mind, most employers offer some sort of time off / leave as a benefit. A benefit -is- a form of compensation! And it's the employee's -not- the employers. Consider this: As you work over time, you receive both a paycheck and some allotment of leave per check as compensation for time worked previously. This leave allotment is held in trust - a bank account if you will. That allotment has monitary value. And it is payed out of the "trust" back to the employee.
While employers like to "say" they have authority to deny leave, the truth is, they DO NOT. It is not their time to administer. It is the employees.
With that said, labor contracts do sometimes make provision, or stipulation regulating leave. Upon hiring, usually a code of conduct, or policy and procedure manual will make reference to how leave is supposed to be administered. Be very careful! Just because it is written, doesn't always make it legal.
My recommendation to anyone having issues with being denied leave, really needs to discuss this matter with their Union leadership, legal counsel, or contact the nearest U.S. Dept. of Labor office.