Working double jobs

If I work 2 jobs, is there any way one employer would find this out unless I tell them? Especially if I use 2 different computers for each job

I have no problem letting my companies know I have 2 jobs, but I know they won’t allow it even though there’s no mention of it in the official company policy (because why would any non-minimum wage job be ok with it). I’m thinking this is a case of asking forgiveness instead of permission.

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