Re:Ask HN: Can I fork my open-source project I created under...
by ncmncm on Thursday September 24, 2020 @02:06PM
(#24581546)
In many US states, provisions in any contract forbidding you to take certain other jobs are entirely unenforceable. In some states it is illegal even to ask you to sign such a contract (although many employers do anyway), but in most others where they are unenforceable, employers can still ask and hope you are fooled.
There are probably whole countries that forbid these contract provisions, or forbid enforcing them.
Don't assume that any particular right you signed away to get a job is really gone. Ask a local lawyer. Expect to be surprised. In many cases, even when there is no specific law, case law has interpreted such clauses very restrictively, making them de facto unenforceable for, e.g., anybody below company officer level.
That said, as others are trying to point out, there may be other issues that are NOT related to the code. You may have restrictions in which field you work and for what client. In this case your employer must approve your employment elsewhere and if they prevent it they must pay a significant portion of your salary until you find a suitable different employer in a different field (at least that's what my contract says but I am European so it might be different in the States).
Anyway, the simple case of using the code is allowed to you under MIT license.