The Irish Council for Civil Liberties has called on the Minister for Justice to explain why he used executive powers to exclude a US pastor from visiting Ireland.
Charlie Flanagan signed an executive order banning Steven Anderson from travelling here.
The pastor, from Arizona in the United States, had planned to host a preaching event at an unknown location in Dublin on 26 May.
He is the first person to be excluded from Ireland in the 20 years since the exclusion power came into law.
Liam Herrick, Executive Director at the Irish Council for Civil Liberties, said this seems to be the exercise of a very exceptional power, and that we need more information about how this decision was made.
"The law requires that a decision of this type must be necessary and must be in furtherance of public policy," he said.
"The standard of necessary is a very high threshold, so we need to know why this was necessary or the only way of dealing with this particular difficulty, and we also need to know what is the public policy that requires this step."
"Because this decision affects fundamental rights in such an important way, we believe there's a duty to give reasons in this case too".
He said there is a wider question about what we and what this individual or his organisation are trying to achieve.
"Sometimes being banned serves their political ends. Sometimes confronting hate speech and messaging of this type directly, protesting and ridiculing what's being said can actually be more effective in the longer term," he said.
"The use of exceptional legal powers needs to be very tightly defined and tightly explained and I think we need more information from the Minister on this".
Mr Herrick said that there are weaknesses in other areas of our laws that would probably be a more effective and appropriate way to deal with these issues.
"Ultimately, incitement and public order offences coming from speech are policing matters that are appropriately dealt with by our police. We haven't felt the recourse to take exceptional steps up to now, so we have to question why it is necessary on this occasion," he said.
A spokesperson for the minister said he would not be commenting further, other than to confirm that he signed the order to exclude Mr Anderson "with immediate effect in the interest of public policy".
LGBT Ireland is one of the groups involved in setting up a petition over Mr Anderson's planned visit, which got 25,000 signatures.
It said Mr Anderson has a "track record in spreading very dangerous and distressing hate speech" and it set up the petition because it "felt it was important call that out and make a stand".
CEO of LGBT Ireland Paula Fagan said they were relieved by Mr Flanagan's decision, but has called for new legislation around hate speech and hate crimes in Ireland.
"Unfortunately we don't have very effective hate speech legislation in Ireland, and we don’t have any legislation or any law in Ireland around hate crime," she said.
"In the absence of those, we called for this ban, but going forward we'd like to see very robust legislation in place so people know what the parameters are around what people can say and what is unacceptable and dangerous in terms of speech".
She said the group is working with the Department of Justice on an LGBT inclusion strategy.