Can I legally tell an employer I cannot work for them?

If you are not under a contract, you are normally an "employee at will". This means you can quit or be fired for any or no reason so long as it does not violate some discrimination or other law. Under the facts you describe, you can be asked to come in at any time and if you don't, you can be terminated. However, if the termination is not for "good cause", it will not disqualify you for unemployment compensation if you are otherwise eligible. You are also able to tell this employer that you can't show up, but you would be risking termination without legal recourse.

Yes, it's legal for you to tell the employer that you cannot work for them under those conditions, but it's also perfectly legal for them to ask you to do so, and likewise legal for you to quit or for them to fire you. As long as you're making at least minimum wage for the hours that you are actually working, there's no other violation of Oregon law here that I can see. If you're only making $10 for 2 hours of work, that would be a violation. But, the law concerns gross amounts not net amount. So, travel time or the balance between this job and other job opportunities don't factor into the legality of the work itself. Neither does a flexible or weather-based scheduling system. It may not be financially viable for you to perform this job in certain circumstances, of course, but that's not a legal issue so much as it is merely a practical issue.