Together For Yes has confirmed its crowdfunding page was hacked in a cyber attack on Wednesday evening.
The umbrella group, calling for a Yes vote in the Eighth Amendment referendum, claim this was carried out by "an unknown Irish-based entity."
The crowdfund initiative was shut down for 30 minutes after the company hosting the website was attacked.
The group says the attack took place at 5.45pm, which would "ordinarily be a peak time for donations."
The company which hosts the crowdfund webpage, Causevox, said it experienced a DDOS (Distributed Denial of Service) attack from within Ireland.
This momentarily disrupted internet service and brought down its entire global platform.
Causevox also hosts crowdfund webpages for Amnesty and Terminations For Medical Reasons.
Sarah Monaghan, Together For Yes spokesperson, said: "We are continuing to investigate this extremely serious incident and are actively consulting security experts in the field to help identify the specific source of the attack, and have made a report to gardaí.
"Together For Yes is a national grassroots movement which relies on small donations from large numbers of people
"Our crowdfund initiative is a core element of the manner in which we resource our campaign and therefore we would take extremely seriously any attempt to undermine it."