The Affordable Care Act contains at least two economically distinct taxes on labor market activity. Even the experts on the law have failed to recognize all of them.

The Affordable Care Act tries to make health insurance affordable by offering means-tested subsidies and tax credits to households so they can make their payments for monthly health insurance premiums and out-of-pocket health expenses like deductibles and copayments for medical services.

This assistance is means-tested because higher-income households get less assistance than lower-income households. As a household’s income rises, it has to pay more for the same coverage. As a matter of economics, it wouldn’t have been much different if the law had given assistance to all households and then paid for it with a new income tax that was capped once household income hits 400 percent of the federal poverty line.

Naturally, income taxes discourage people from doing the things that create income. This is not to say that everyone responds to every tax, just that the average result of an additional income tax is less income.

Economists have long understood and publicized the implicit income taxes that come with attempts to make health care affordable. As my fellow Economix blogger Uwe Reinhardt put it 20 years ago (in an article with Alan B. Krueger) about one specific subsidy plan, health insurance premium assistance “would present millions of low-income American families with total marginal tax rates in excess of 75 percent.” Professor Reinhardt also noted recently that the marginal tax rate implicit in any particular health insurance proposal depends very much on the features of that plan.

The Congressional Budget Office also highlighted this issue as the Affordable Care Act was going through Congress. Daniel P. Kessler, a Stanford professor, also discussed it in a commentary

Under the Affordable Care Act, only a small minority of workers is expected to get subsidized coverage. So economists concluded that aggregate labor market effects of the new law would be minimal.

I would agree if the implicit income tax were the only new tax on labor market activity in the new law. But there’s more: The Affordable Care Act also contains a new implicit tax on employment that affects far more people than its implicit income tax does.

Income taxes and employment taxes are not the same, because the income tax is based on income and the employment tax is based on employment. Two households with the same family structure (in number and age of family members) and annual income who live in the same county will not necessarily get the same assistance from the Affordable Care Act. The household that is employed more months of the year is likely to get less assistance (and maybe no assistance) from the new law, because the law requires that, during the months that they are employed, full-time workers get health coverage from their employer before they turn to the new health insurance marketplaces for federal government subsidies.

To put it another way, even if the health insurance subsidies in the Affordable Care Act had been a specific dollar amount that was not phased out with household income, the law would still act as a tax on employment because most workers could not get the assistance during the months they were at work.

This new implicit employment tax will apply to tens of millions of workers who are offered health insurance on their job and to millions of non-employed persons who are considering a position that offers coverage.

(The new employment tax also changes the types of jobs that are created and accepted by workers, but this effect does not prevent the law from reducing employment, as Trevor Gallen and I explain).

As far as I know, before this month the only place that one could read about the Affordable Care Act’s new employment tax was in this paper by David Gamage, in posts I have written for this blog, in my 2012 book or in a 2013 paper. Even though the consequences of the law have been debated at least as far back as 2009, the law’s advocates have yet to acknowledge the new implicit employment tax, let alone estimate the number of people who will face it.

But in a recent paper, the Congressional Budget Office has joined me in explaining that it’s not just the implicit income tax that will contract the labor market. As the paper puts it, “The loss of subsidies upon returning to a job with health insurance is an implicit tax on working,” adding that the effect of the new tax is “similar to the effect of unemployment benefits” (see Page 120).

Once we consider that the new law has an employer penalty, too, the labor market will be receiving three blows from the new law: the implicit employment tax, the employer penalty and the implicit income tax. Regardless of how few economists acknowledge the new employment tax, it should be no surprise when the labor market cannot grow under such conditions.

Casey B. Mulligan is an economics professor at the University of Chicago. He is the author of “The Redistribution Recession: How Labor Market Distortions Contracted the Economy.”