Valid, but not all companies clearly mention what's allowed and what's prohibited in terms of second-job employers.
A few years ago, they hired an experienced barista for our Target Starbucks. The new barista kept telling people she still worked at Starbucks as well as at our Target Starbucks. When I asked and she said it was inside a QFC supermarket (Kroger-owned), she didn't think she had to disclose that her actual employer was QFC/Kroger.
This barista even frequently encountered and served her clientele from her QFC Starbucks who were shopping at our Target. She was very friendly and courteous, but I joked with her that she really worked for a competitor, QFC.
A couple of months later, she was gone. I've wondered if she got into some sort of corrective situation - which was elevated to a termination - after HR routinely double-checked the original job application where she inaccurately claimed to be a Starbucks employee, not a QFC/Kroger employee.