What are the space requirements?
The law requires employers to provide a place that is not a bathroom. It must be completely private so that no one can see inside the space and no one is able to enter the space while it is being used. It also must be "functional [useable] as a space for expressing breast milk."
Employers are not required to create a permanent dedicated space for breastfeeding employees. In many workplaces, there is no unused space. In that case, the employer could instead give you access to a space normally used for other things (like a manager's office or storage area).
As long as the space is available each time you need it, the employer is meeting the requirements of the law. If there are no breastfeeding employees, the employer does not need to maintain a space.
If more than one breastfeeding employee will need the space, mothers can develop a room-use schedule or the employer can install privacy curtains or dividers so that the room can be used by more than one person at a time. The dividers must ensure that each station is completely private.
If the space cannot accommodate all mothers when they need it, the employer is not meeting the requirements of the law.
The Business Case for Breastfeeding recommends that at a minimum, employers provide a safe and private space with a chair and a small table or shelf to set the breast pump on. An especially useful space could include an electrical outlet, a door that can be locked from the inside, a sink, and/or a refrigerator located near the pumping space. Though not required, these additions can help shorten your break time because you will not need to travel to another area to wash your hands, clean your pump parts, and store your milk.