Yes, a company can do this. The fact is that most employment relationships are "at will", which means that a business can set the conditions of work much as it sees fit. This includes mandating that certain educational requirements be met, even if this was not a previous requirement. This is true so long as such action does not violate the terms of an employment contract or union/collective bargaining agreement. Also, a worker's treatment must not constitute some form of actionable discrimination or retaliation. Accordingly, you can accept the situation, complain and risk terminstion, or quit.