The shoes, bearing the trademark red sole that Christian Louboutin originals are known for, were shipped from China, according to officials at the Los Angeles/Long Beach seaport complex.
Four shipments were seized on Tuesday, while another shipment was seized July 27, says U.S. Customs and Border Protection (CBP) spokesman Jaime Ruiz.
Customs agent Elizabeth Ortega told Reuters the French designer's high-end pumps, which are made in Italy, sell for as much as $1,200 a pair.
The agency says the 20,000 knock-offs collectively are worth a total of no more than $57,000, based on a manufacturing cost of just under $3 a pair.
It's believed the counterfeit shoes were to be sold mostly to online buyers. Now, they're expected to be destroyed.