As unfair as it seems, yes you can be terminated for not being adequately certifed, even if your employer was or should have been aware of that fact. This is true unless the action is some way consitutes some form of legally actionable discrimination (which it does not appear to) or if it violates the terms of any employment contract/union agreement. Otherwise, your employer is free to set the conditions of your employment much as it sees fit. Bottom line, in an "at will" work relationship, an employee can be discharged for any reason or no reason at all, with or without notice.