Independent TD Danny Healy-Rae has been strongly criticised for comments he made suggesting a possible link between autism and vitamins.
Speaking during a Dáil debate on special education places, the Kerry TD said more should be done to find out what was causing an increase in autism cases.
He said there appeared to be more presenting than in his younger days.
"I am wondering what it is, and I have asked this question here before in different debates. Is there something causing it?
"Is it lack of some vitamins or what is it? We need to address that part of it as well because there could be something that is causing it."
Sinn Féin spokesperson on Special Education Shónagh Ní Raghallaigh has called on the deputy to withdraw his remarks.
"I was genuinely shocked at his remarks that I deem to be extremely disparaging and completely unfounded," she said.
"Spouting conspiratorial beliefs on the floor of the Dáil on such a sensitive topic is unacceptable."
The As I Am charity described Mr Healy-Rae's contribution as unhelpful and misinformed.
In a statement it said: "We would ask all Oireachtas members to think about the impact of their words before they use their platform to add to the pervasive stigma, myths and hurtful stereotypes that not only cause hurt but create barriers to diagnosis and support and pose broader public health concerns."
The charity also pointed out that autism is a natural variation in human neurology adding that there are not more autistic people than in the past but there are more people accessing diagnosis.
Sinn Féin has called on Mr Healy-Rae to retract his statement and to apologise to families who were sitting in the Dáil gallery at the time.
Ms Ní Raghallaigh has also written to the Ceann Comhairle asking that she facilitate this request.
