This is a violation of Title VII of the Civil Rights Act of 1964
UNLAWFUL EMPLOYMENT PRACTICES
SEC. 2000e-2. [Section 703]
(a) Employer practices
It shall be an unlawful employment practice for an employer -
(1) ...to discharge any individual, or...discriminate... with respect to his compensation, terms, conditions...of employment, because of such individual's race...or national origin
In other words, companies cannot fire US workers and hire foreigners in other countries instead, for any reason.
Since companies are firing US workers and replacing them with non-US workers in other countries based on paying cheaper salaries, they are breaking the above law.
This needs to be (retroactively) enforced by the Attorney General.