This is super incorrect; if anything, employer-based health insurance strengthened the unions' ability to negotiate for their workers. As a sibling comment mentioned, the major catalyst was WWII wage controls:
> During World War II, wage and price controls prevented employers from using wages to compete for scarce labor. Under the 1942 Stabilization Act, Congress limited the wage increases that could be offered by firms, but permitted the adoption of employee insurance plans. In this way, health benefit packages offered one means of securing workers.
> In the 1940s, two major rulings also reinforced the foundation of the employer-provided health insurance system. First, in 1945 the War Labor Board ruled that employers could not modify or cancel group insurance plans during the contract period. Then, in 1949, the National Labor Relations Board ruled in a dispute between the Inland Steel Co. and the United Steelworkers Union that the term "wages" included pension and insurance benefits. Therefore, when negotiating for wages, the union was allowed to negotiate benefit packages on behalf of workers as well. This ruling, affirmed later by the U.S. Supreme Court, further reinforced the employment-based system.
None of what you quoted here offers a different origin of employer-linked health insurance, and it avoids even mentioning that they were excluded from taxation. The fact that they weren't included in wage caps is just another benefit granted to employers.
> if anything, employer-based health insurance strengthened the unions' ability to negotiate for their workers.
In what way does having more that needs to be negotiated strengthen unions? You've heard the punchline without hearing the joke: why were unions prevented from negotiating pension and insurance benefits before 1949?
If you reversed the original sin of sheltering wages paid in the form of health insurance from taxes, you'd see stronger unions the next day. The biggest battle fought during the ACA war was about the possible taxation of "Cadillac" health plans, and ACA lost.
