The Affordable Care Act amended section 7 of the Fair Labor Standards Act ("FLSA") to require employers to provide "reasonable break time for an employee to express breast milk for her nursing child for 1 year after the child's birth each time such employee has need to express the milk."
The employer does not have control over the number of times the employee must express breast milk. Employers are also required to provide "a place, other than a bathroom, that is shielded from view and free from intrusion from coworkers and the public, which may be used by an employee to express breast milk."
However, the law does not require that this time be paid. Therefore, you can ask the employee to clock out before she leaves to pump and clock back in once she is ready to return to work.
All employers (regardless of the size or number of employees) must comply with the break time for nursing mothers. However, businesses with fewer than 50 employees may be able to apply for an undue hardship exemption. To receive an exemption for an employee, the employer must prove that providing these accommodations would cause "significant difficulty or expense when considered in relation to the size, financial resources, nature or structure of the employer's business."
Until an exemption is granted by the Department of Labor, the employer must comply with the law.