Also cleaning and administration services wouldn't be contractors, but services bought from another company. So that wouldn't count either.
If you close all reasonable loopholes and make your intent clear when you write the law, a judge (at least here in the US, I know the UK has a slightly different system) is not going to say "Oh, that's undefined behavior, you get a free pass."
He or she is going to say "That's undefined behavior, but you're trying to circumvent what was clearly the intent of the law. Bring yourself into compliance or face further penalties."
For all the places that I've worked, the cleaners have always been part of another company, one that was contracted to provide cleaning services. There's also firms and contractors that provide bookkeeping services for small businesses. I'm sure a lot of other administrative tasks could be outsourced as well.
Having these services provided by other companies would raise the minimum salary in a company quite a lot.
The other thing companies do is set up plenty of shell/thin corporations around the world, assign the IP rights to those in minimal tax countries, and then charge massive internal fees so that all the rest of the organisation barely makes a profit. This sort of thing seems to be the same level of loop-hole as setting up multiple companies so that the CxO's can get paid more.
Of course that's forgetting that most of the CxO pay is actually in stock and options, and not so much is in cash, so I don't know how much a law capping CEO pay would do. Some notable CEO's have actually taken just $1 of actual cash for payment (because legally they have to be paid something to receive company perks).
All it takes to end this practice is for the tax authorities to take a dim view of it.
Starbucks and Google were both caught by this and although they didn't pay a fine as large as they should have done, with a nod and a wink, they did end up paying more.
The economic system is nowhere near as immutable to change as certain people would like you to believe.
The swift reaction by BlackRock to the government simply making noises in particular was noteworthy:
https://www.theguardian.com/business/2017/jan/15/blackrock-d...
It's not so easy to apply to a law written in terms of concepts like "two employees of the same company", because "company" is itself something that only exists as a legal construct and "employee" already has a specific legal meaning that's significantly different from its common-sense one.
Wikipedia's background is weak, but Northern Securities Co. v. United States in 1903 [1], one of the first major anti-trust prosecutions, was equally novel by the fact that the US government was choosing to prosecute it at all.
The Sherman Anti-Trust Act (1890) had been on the books for better than a decade. Under a unified government, applicability is rarely as much of a question as enforcement.
[1] https://en.m.wikipedia.org/wiki/Northern_Securities_Co._v._U...
It's surprising how often we had cause to (although maybe we're both borderline).
For example in clothes manufacturer, which contracts out the making of its clothes to a company in another country. Would the people employed by that other company be counted?
Maybe it's naive to think its as simple as being slightly more verbose: "Salary tied to lowest paid employee or contractor"