Brittni Medina posted the picture on a Facebook page dedicated to breastfeeding moms. In the post, she says that she was standing in line to take a picture when her 10-month-old got hungry, so she took off her top and decided to nurse him.
In the photo, you can see two women in the background, angry - one of them crossing her arms - as Medina smiles at the camera and feeds her son.
"Well these ladies were so angry by it my husband just had to take a picture. Peep the haters," she wrote.
Medina's post instantly went viral and has been shared more than 1,000 times. Several of the comments are positive and encouraging, but not all.
Overall, Medina said she's grateful for the support.
"I've gotten both negative and positive but the support has outweighed the negative," Medina said. "I'm so proud of all the moms losing the cover. The law fully supports us."
In California, mothers are legally allowed to breastfeed in public.