Facebook prohibits users from posting content that "contains nudity".
Website tera.ca carries 389 breastfeeding photos banned by Facebook.
Facebook told news.com.au that most breastfeeding photos posted on its site complied with its terms of use.
But some "contain nudity - for example, an exposed breast that is not being used for feeding - and therefore violate our terms".
Ms Williams said Facebook's actions were bizarre and out of kilter with society.
"It reduces even further the images of breastfeeding women. It has a huge impact. They [Facebook's operators] need to accept the normality, the everyday-ness of a woman breastfeeding her baby.
"I'm sure if someone put up a photo of a woman bottle-feeding a baby they wouldn't give it a second thought."
Ms Williams had earlier spoken out in support of the removal of a bottle-feeding clip featuring All Black Piri Weepu from a smoke-free advertisement.
Weepu was filmed for a day, including the brief clip of him bottle-feeding his 6-month-old daughter Taylor, for television ad for the Health Sponsorship Council, a Government public health promotion agency.
The council asked the La Leche League and Plunket about the bottle-feeding section. Public health groups blitzed the council with emails seeking the clip's removal.
But after the story appeared on nzherald.co.nz yesterday, there was an outpouring of reader criticism of La Leche and the council.
Many thought pulling the clip was ridiculous kow-towing to official views and weakened fathers' rights to bottle-feed their babies.
"It's a natural, loving thing for a father to do," said "Trotski".
However, Barbara Taunton-Clark, of the Auckland Breastfeeding Network and the lactation services manager at the Birthcare maternity centre, said that in light of "all the money the Government has put in to promote breastfeeding and [Weepu's] being such a high-profile person, it would just undo some of that good work".
"People are very vulnerable with what they see. [They might think], 'If it's alright for them, it's alright for me'."
Birthcare's website says "breast is best", but Mrs Taunton-Clark said the hospital's policy was to support a woman's choice, whether it was breastfeeding or bottle-feeding.