In December, the Congressional Budget Office (CBO) released a report estimating that Obamacare would shrink America's economy by the equivalent of about 2 million jobs over the next decade.
Despite the headline job-loss estimate, the CBO wasn't really saying that the law would kill off millions of jobs in the sense that employers will fire people or eliminate positions. Instead, as with a previous report estimating a labor force reduction equal to about 800,000 jobs, the CBO predicts that people will scale back their hours or quit work entirely, since the law allows them to do so without losing their access to health insurance.
What this means is that, thanks to Obamacare, the U.S. labor force is likely to be significantly smaller a decade from now—that there will be less work performed and fewer people employed as a result of the law. But it won't be because Obamacare made those positions unavailable to people who want them; it will be because Obamacare created a set of circumstances in which some people chose to leave jobs, or reduce the number of hours they worked.
Obamacare isn't a job killer, then, so much as it's a work killer: a change in the nation's benefits and incentive structure that makes work less desirable for millions of people.