Cymdeithas yr Iaith refuses to answer questions from UKIP AM
A Welsh language campaign group has been told it cannot give evidence to the assembly's culture committee as it will not answer questions from UKIP.
Cymdeithas yr Iaith Gymraeg claimed UKIP "promoted and tolerated prejudiced attitudes" to minority groups.
The society said it was "undemocratic" to withdraw the invitation.
Committee chairwoman Bethan Jenkins said witnesses could not choose who could ask questions, while UKIP's Neil Hamilton told Cymdeithas to "grow up".
Mr Hamilton, who leads his party in the assembly, is the only UKIP member of the committee.
Representatives of the society had been invited to give evidence on Welsh language standards on Wednesday.
Cymdeithas chairwoman Heledd Gwyndaf called the dropping of the invitation an "undemocratic decision" and "a dreadful reflection of the state of politics today".
She accused members of the committee of "embracing UKIP's prejudice with open arms", claiming: "They are blocking a platform for us, who support rights for the Welsh language and for other minorities.
"UKIP has promoted and tolerated prejudiced attitudes against a number of groups in our society - gay, lesbian, bisexual and trans people, ethnic minorities, migrants, people with HIV - and the Welsh language," Ms Gwyndaf added.
"We cannot treat them like any other party."
Ms Jenkins, Plaid Cymru AM for South Wales West, said: "There's every right for them [Cymdeithas] to come on the basis that every elected AM has the right to ask them questions if they so wish."
She said it was "odd at best" to call the submission of written evidence "undemocratic" and an "insult" to those who have provided evidence in such way.
"For the time being, the people of Wales have given UKIP a democratic mandate to be here and we have to respect those voters' wishes," Ms Jenkins said.
She added that she consulted all members of the committee after she was informed that Cymdeithas would refuse to take questions from any UKIP AM.
"The unanimous view of those who responded was that it was for the committee to decide who should ask questions and not witnesses," she said.
"On that basis, we wrote back to Cymdeithas and said we would consider its submitted written evidence to our inquiry instead."
Mr Hamilton said he was looking forward to speaking to the group, and had read their written evidence "with great sympathy", but said the organisation should "grow up".
"They do no favours to the Welsh language by their puerile display of ignorance and bigotry," he said.
The UKIP group leader said the assembly "cannot be dictated to by extremists".
Pointing to the 13% of Welsh voters who backed UKIP in May's assembly election and the 52% who voted for Brexit in June, he added: "It is bad politics for Cymdeithas yr Iaith to insult them as prejudiced.
"I personally support the Welsh Government's aim of making Wales a bilingual nation and I hope Cymdeithas yr Iaith will soon grow up."
An assembly spokesman said: "It is not for witnesses to dictate to an assembly committee who is allowed to ask questions.
"Decisions about inviting witnesses to give evidence are for individual committees to make on a case-by-case basis."