Looks like one of the major criticisms of Obamacare has not come to pass.

Employers have not been cutting workers' hours to escape having to provide them with health insurance, a new ADP Research Institute report has found.

"For all the talk, there have been very small shifts in part-time hiring...almost statistically insignificant," said Christopher Ryan, vice president of strategic advisory services at ADP, a human resources consulting firm.

Obamacare mandates that companies offer coverage to all employees who work more than 30 hours a week. Critics said this rule would prompt employers to reduce workers' schedules to avoid the mandate, which kicked in for large employers this year and will take effect for those firms with 50 to 99 employees next year. (Companies with fewer than 50 workers are exempt.)

ADP found that the share of the labor force working fewer than 30 hours remained virtually the same between 2013 and 2014. Same goes for workers employed 30 to 34 hours a week and more than 35 hours a week.

Related: I'm quitting my job. Thanks Obamacare!

This remained true across industries. Part-time employment barely budged in fields including leisure and hospitality (about 43%) and education and health services (about 27%). And it actually declined in wholesale and retail trade, from 24.1% in 2013 to 21.3% in 2014.

These results are in line with data from the federal Bureau of Labor Statistics, which shows part-time employment remaining flat or declining slightly between 2010 and 2015, Ryan said.

One reason why employers aren't reducing workers' hours is because the economy is improving. So there's a greater demand for labor. Some companies interviewed by ADP said they may increase their part-timers' hours to retain talent and reduce training costs.

Related: Employers aren't really cutting health benefits

"When it comes to staffing, employers are going to put their business and customers first," Ryan said. "The law of supply and demand is trumping other considerations."

Obamacare, however, will likely reduce how much people work overall ... but it will be a voluntary decision, according to a Congressional Budget Office report released last week. Some workers will opt to quit because they can now get health insurance through the Obamacare exchanges. Others will limit their hours so they can keep their eligibility for subsidies and Medicaid.