Not just politically impossible, illegal:
>> World War II disrupted those trends. As demand for everything — particularly labor — climbed, Congress passed the Stabilization Act of 1942, which allowed the president to freeze wages and salaries for all the nation's workers. A day after its passage, President Franklin Roosevelt issued an executive order invoking these powers, which applied to "all forms of direct or indirect remuneration to an employee," including but not limited to salaries and wages, as well as "bonuses, additional compensation, gifts, commissions, fees."
But there was an exemption of massive proportions slipped into a fateful clause: "insurance and pension benefits" could grow "in a reasonable amount" during the freeze."
- https://www.chicagotribune.com/opinion/commentary/ct-obamaca...
And, relevant to today's discussion:
>> By slapping corporations with tax rates of 80 or even up to 90 percent on any profits in excess of prewar revenue, Congress all but guaranteed a frenzied search for loopholes.
Also interesting to note that the change in question wasn't a switch from workers paying for their own health insurance to it being paid for by employers. Prior to WW2 less than 10% of Americans had any form of health insurance, by the end of the war it was close to 30%.