The Affordable Care Act will cause millions of Americans to pay more for their health insurance, lose their coverage, or have their work hours curtailed, according to Stanford business and law professor Daniel Kessler.

People who have individual and small-group health insurance are particularly vulnerable, he writes in The Wall Street Journal.

“These policies are most affected by Obamacare's community-rating regulations, which require insurers to accept everyone but limit or ban them from varying premiums based on age or health. The law also mandates ‘essential’ benefits that are far more generous than those currently offered.”

Oliver Wyman consultants estimate that single adults aged 21-29, earning 300 to 400 percent of the federal poverty level and holding individual health policies will endure a rate hike of 46 percent, even after premium assistance from tax credits.

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“Higher premiums are just the beginning, because virtually all existing policies in the individual market and the vast majority in the small-group market do not cover all of the ‘essential’ benefits mandated by the law,” Kessler writes.

“Policies without premium increases will have to change, probably by shifting to more restrictive networks of doctors and hospitals.”

In addition, the Congressional Budget Office estimates that Obamacare will cause 3 million people to lose their insurance completely in 2014. And it expects that 6 million will have to pay the individual-mandate tax penalty in 2016, because they don't want or can’t afford coverage.

Some workers will see their hours cuts, because employers aren't subject to a tax penalty for employees who work less than 30 hours per week, Kessler says.

“In total, it appears that there will be 30 million to 40 million people damaged in some fashion by the Affordable Care Act,” he writes. “When that reality becomes clearer, the law is going to start losing its friends in the media.”