Many managers believe they have the power dismiss insubordinate employees, no matter how unreasonable the request.  The courts have consistently shown this not to be true.
Daniel Lublin illustrates this point in his weekly column in the Metro titled, “Employers shouldn’t mess with your vacation plans”.
On her way to a family reunion, Lerae Bigelow received a phone call from her boss demanding that she come in to work.  Believing this to be unreasonable, since she had booked the time off and explained that it was too late to reschedule, she refused and took her vacation as planned.  Upon her return, she was dismissed via text message and received no severance.
Below are some questions to consider regarding employer demands:

• Job duties: How far outside of the scope of your regular duties is the task?
• Safety: Do you consider the work to be unsafe? If so, the Ontario Health and Safety Act permits you to refuse without reprisal.
• Reasonableness:  How reasonable is the request? How reasonable would your refusal be? 
• Past behavior: How clean is your employment history?  Is this your first refusal or have you lost count?

All of these questions matter to the courts.  Bigelow was successful in her claim for wrongful dismissal, but employees should be careful when dealing with employer demands.  As unreasonable as a request may be, your reaction could determine whether or not you get severance.
Other vacation-related articles:
Retirement home employee fired for going on vacation with a resident
Employee fired after mistakenly booking the wrong day off