It may depend on what type of benefits you are referring to. For instance, are you concerned about an optional benefit, such as vacation, or health insurance obligations under the Affordable Care Act?
Paid vacation time and holidays are optional, employer-provided benefits. Employers are not required to offer these benefits to part-time employees, unless there is a union agreement. Some employers choose to offer paid vacation and holidays to part-time employees who work a set number of hours. Other companies provide part-time employees with these benefits on a pro-rata basis.
Mandatory paid sick leave (under the Healthy Workplaces, Healthy Families Act of 2014) requires employers to provide paid sick leave to any employee who has worked in California for the same employer for 30 days within a year from the beginning of employment. There are only a few limited exceptions. Part-time employees are covered by this law. The law sets specific requirements regarding accrual and use of the paid leave.
Company insurance plans, pension and profit-sharing plans and cafeteria plans are treated differently.
These benefits are highly regulated by a comprehensive plan document that must be approved by the Internal Revenue Service (IRS) and meet non-discrimination rules of the Employee Retirement Income Security Act (ERISA). These types of plans involve non-taxable dollars; therefore, there are significant penalties for non-compliance.
Each plan is required by law to clearly spell out eligibility and once an employee has met the eligibility criteria, he/she should be allowed to participate in the plan. For example, if the company's group health insurance plan states that employees are eligible for coverage if they work 30 hours per week and have completed 30 days of employment, then the company would be in violation of its group insurance plan by not including those part-time employees who qualified for coverage, irrespective of any company statement to the contrary.
Moreover, the federal Affordable Care Act (ACA) has specific definitions of full-time versus part-time employees that need to be considered when reviewing the shared responsibility provisions of the ACA.
You can find more information on the
Federal Health Care Reform of the ACA, differences between
Full-Time vs. Part-Time Employees and
Required and Optional Benefits in the HR Library.