Scott Gottlieb explains:
As workers transition from part time work (without benefits) to full time work (with health benefits) many workers will actually lose income in the form of the subsidies that they will have to forgo (and the additional fact that lower wage workers, who are in lower tax brackets, won’t benefit as much from the implicit subsidy they will get from the special tax treatment of health benefits that they receive by purchasing their health insurance through their employer).
CBO states, in reference to these impacts, that the “exchange subsidies effectively constitute a tax on labor supply for a broad range of workers.” CBO goes on to state that forgoing ObamaCare subsidies and returning to full time work with health benefits (for lower wage and middle class workers) amounts to an average, implicit tax of about 15% paid by each worker. CBO does note that these considerations only affect a segment of the workforce — specifically the middle class and working class who earn annual incomes that put them below 400% of the Federal poverty level (about $95,000 for a family of four). But that represents a large portion of the labor market.