Many employers define different classes of employment within their organization.  These classes – full-time, part-time, exempt etc. – are used to determine benefits which are offered to different types of employment given their skills, tasks, responsibilities, and hours worked.
For purposes of these distinctions, full-time employment warrants the most benefits of the employment classes.  This usually means access to vacation and all forms of employer-sponsored benefits such as health insurance.
Full-time employment has always been defined as 40 hours or more per week.  That is because the regular work week consists of 5 days of 8 hours of regular-pay work.  Anything more than 8 hours on any given day was overtime.  California state law endorses this simple definition as well (see Labor Code § 515(c)).
However, a little-known section in the Patient Protection and Affordable Care Act (a/k/a “Obamacare”) defines “full-time” work as averaging only 30 hours per week.  The IRS released Notice 2012-17 in March 2012 to address some questions regarding the definition of a full-time employee for health care reform purposes. Under health care reform, determining whether an employer is subject to a penalty for not sponsored a group health plan, how to calculate any penalties and when the employee is eligible to participate in the employer’s health plan are all contingent on determining whether the employee is full-time or not. In Notice 2012-17, the IRS confirms that an employee is considered full-time if he “averages at least 30 hours per week”.
This will affect a number of employers who use part-time workers (i.e. those working less than 40 hours per week).  Many small business employers trimmed their full-time payroll in order to comply with the anticipated Obamacare rule that says businesses with 50 or more workers must provide health insurance or pay a fine.
However, the section known as the “employer mandate” actually requires any business with 50 or more full-time employees to provide at least the minimum level of government-defined health coverage to those employees, where “full-time” is described as 30 hours or more.  If an employer has 50 or more of these newly-defined “full-time employees” and does not offer health insurance, it must pay a penalty per employee for each month it does not offer coverage.
Its enforcement appears to be even more onerous.  Once in effect, it provides guidelines on how to treat current employees.  In regulations recently issued by the IRS, employers are provided with instructions on how to account for which workers are full-time and which ones are not.  Under these standards, employers are forced into a “look-back” period of between 3 and 12 months to measure if an employee has worked an average of 30 hours per week.  If an employee has worked 30 hours per week during this time, the person would count as a full-time employee for at least the next six months, regardless of how much they work, thus preventing employers from cutting hours to avoid the mandate.