Amazon has limited sales of emergency contraceptive pills as demand spikes following last week's U.S.

The company has placed a temporary quantity limit of three units per week on emergency contraceptive pills, Amazon confirmed to CNBC.

A review of emergency contraceptive pills sold on Amazon showed varying quantity limits.

Walmart said many of the chain's products have online purchase limits that can change "during times of fluctuating demand." Walgreens said purchases of emergency contraceptive pills were not being limited.

Emergency contraceptive pills, often referred to as "morning after pills" and sold under the Plan B brand, can be purchased over-the-counter and without an ID or prescription.