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Though more Americans today are clocking in a less-than-40-hour workweek than a decade ago, this trend can't be blamed on the health reform overhaul—at least not yet, a new study found.

The analysis, done by the Employee Benefit Research Institute, found that the movement toward shorter work weeks was underway before the health law passed in 2010. The percentage of people working less than 40 hours has actually dropped slightly since then, according to the study.

So the study attributes the trend to the recession rather than the health reform law.

The finding is important because there is some concern that firms may cut back on worker hours to get out of the employer penalty that was to be put into place by the law. Firms with 50 or more employees putting in at least 30 hours a week must offer affordable health insurance to workers or pay a fine. "There are anecdotes about employers talking about cutting hours," says Paul Fronstin, director of health research at EBRI. "Whether or not some went ahead and did it I don't know. But we haven't seen it on a net impact."

The study includes data only through 2012, two years after the law was passed but still two years before the employer mandate was set to kick in. Fronstin says many employers plan in advance, and likely would have started a strategic shift before 2014.

Still, the year the penalty kicks in has been pushed back by President Obama to 2015 or 2016, depending on the size of the employer. So the data for future years may tell a different story. "No question we could see things change in a year or two," says Fronstin.

Overall, though, the study concludes that future workforce patterns may hinge more on unemployment rates and the strength of the economy than the law.

One downside of a gig with less than 40 hours a week is that you’re less likely to have access to company health insurance. Firms have dropped coverage for their part-time workers over the past decade at a faster rate than for those with full time positions. Only 13% of workers putting in fewer than 30 hours a week have health insurance through their job, according to the study.

NOTE: 2012 data. SOURCE: Employee Benefit Research Institute