What would happen if a UK company was hired to build a bridge in Germany and the German government says it cannot bring over Brits to do the job? The Unions would be out protesting about the UK company using "cheap local labour" instead of employing Brits and shipping them over - "turning their backs on our lads".
You cannot have your cake and eat it too.
This is not a matter for law. Law in this case makes for a mess, red tape, central control and eventually prices going up and things here getting less competitive.
Now, I am all for transparency, so if a company will not hire, that should be open to question. It should also be possible for people to have the right to ask if a company uses contractors that will not bother to hire locally, but instead brings in its own people. Companies can refuse to answer, of course, but then what does that say? If the companies lie, then that is a matter of fraud or misrepresentation. No need for new legislation.
Accountability, self responsibility.
The real issue is about the high cost of living in the UK, the hopeless de-education that occurs in "State" Schools, the high levels of tax and waste at all levels of government.
The answer is not protectionism - which I suspect is being called for by the same useful idiots, self-loathers and Fifth Columnists who wee moaning about the prospect of US protectionism - but to make the UK an efficient place to live and do business. Cut taxes, remove unnecessary red tape and regulation, get the State out of Education. It almost goes without saying that a country should not have to go cap in hand to some foreign entity to ask permission to do all this, so out the EU we must be.
The only party that is proposing all the above is the Libertarian Party. All the rest are just window dressing.