> Foreign labour depreciates the wages companies have to pay for employees. It has been shown again and again that concerning quantities of foreign labour is used exactly for that purpose

That's a (citation needed) right there.

The literature on the matter finds little to no effects of immigration on local wages. See the literature review by Kerr & Kerr:

https://www.nber.org/system/files/working_papers/w16736/w167...

Key sentence in the conclusion: "The likelihood and magnitude of adverse labor market effects for natives from immigration are substantially weaker than often perceived. Within the large empirical literature looking at the effects of immigration on native employment and wages, most studies only minor displacement effects even after very large immigrant flows."

What you find in practice is both that immigrants accept lower wages, AND that local wages for natives are unaffected. Which happens because the labor market can generally take in the new labor comfortably.