The flip side is, GM knew its competitor (Ford and Chrysler, for the most part) would get the same UAW bump every two or three years so there was little incentive to fight back. The UAW knew this, too.
Pity they ignored Honda, Toyota, etc that moved in and cleaned their clocks.
The Japanese deliberately limited imports in response to U.S. political pressure in the 1980’s, but subsequently opened plants in the U.S. Automobiles in the U.S. market are at best probably only about 50% domestic content anyway. The assembly step is one of the least value added, compared to production of engines, transmissions and components. When you buy an “American” car it is likely that it was assembled in Canada or Mexico out of parts made in Japan, China and Germany.