Researchers at universities invariably do academic work for conferences, for journals, and for other universities — giving talks, for example. Often they get paid directly for these. This is a fundamental part of how academia works, and has been (in various forms) for centuries.
I worked in Silicon Valley as a sysadmin and programmer in 1996-97 and 2000-2006, at a total of seven different companies. I've also worked professionally at a professional services company, a defense contractor, and freelance for various clients (primarily in the US). I don't think I've ever seen an employment contract that purported to prohibit me from "doing professional work not associated with [my] current job". In some cases I have proposed modifications to confidentiality agreements with the explicit purpose of ensuring that I could moonlight safely (for previous clients, normally). The modifications were accepted.
Having an academic and industrial background myself, I understand that researchers currently do academic work for conferences, journals and so on
The point I was making was that employers could enforce the parts of the contract that allow them to control whom their employees work for. That would, at the very least, not be contributing brainpower to an industry that charges the very same companies / universities enormous sums for access to journals.
While you may not have seen such restrictions in sysadmin/programmer type positions, they certainly exist in several scientific and medical-related disciplines (though I agree that can be waived in certain circumstances).
Researchers at universities invariably do academic work for conferences, for journals, and for other universities — giving talks, for example. Often they get paid directly for these. This is a fundamental part of how academia works, and has been (in various forms) for centuries.
I worked in Silicon Valley as a sysadmin and programmer in 1996-97 and 2000-2006, at a total of seven different companies. I've also worked professionally at a professional services company, a defense contractor, and freelance for various clients (primarily in the US). I don't think I've ever seen an employment contract that purported to prohibit me from "doing professional work not associated with [my] current job". In some cases I have proposed modifications to confidentiality agreements with the explicit purpose of ensuring that I could moonlight safely (for previous clients, normally). The modifications were accepted.