It’s not as straightforward as that. The actual IRS test uses about 20 factors they consider to determine if someone is an independent contractor or an employee.
At any rate, the USC case is an NLRA issue and not an IRS issue, so it’s not exactly the same thing.
It also seems to me that the case of student athletes isn’t as straightforward as determining employment status at for profit businesses. All of these employment tests start with the assumption that someone is a paid worker. The question then becomes simply: is the worker a contractor or an employee?
For student athletes, it seems to me the first question to answer is: are they in fact “workers”? If the answer is yes, then you can move on to asking the question of what type of worker are they (i.e., employee, contractor, volunteer)? But I don’t know that the first question about worker status has been definitively answered yet. Admittedly though, I’m not an expert in labor law.