A councillor branded people protesting against cuts at a Hull City Council meeting "retards" in a rant on Twitter.
Conservative group leader John Fareham made the comment after Friday's meeting, which saw the council approve a controversial £65m savings plan.
It read: "15 hours in council today very hard hitting day and the usual collection of retards in the public gallery spoiling it for real people."
Mr Fareham, who has since apologised, has been criticised by Mencap.
Unison has demanded action is taken over his "disgraceful behaviour".
'Abused for hours'Plans approved at the meeting, which was delayed due to hecklers, included the axing of 1,400 jobs and cuts to day care centres, leisure centres and highway budgets.
The Bricknell councillor said the comment was "misguided", and added in a further Twitter post that it came after he was "abused for hours, returned home to excrement in house and saw intimidation".
End Quote Councillor John FarehamI apologise unreservedly. I got it wrong and I'm sorry”
He added: "I apologise unreservedly for the adjective (sic) in my earlier tweet about the intimidation by some people. I got it wrong and I'm sorry."
Unison regional organiser Steve Torrance said several people with physical and learning disabilities were in the public gallery at the time.
He added: "Not only are Councillor Fareham's remarks offensive and unwelcome generally, they are of particular concern given that members of the public with disabilities were present in the gallery throughout the council debate as well as the people who care for them.
'Offensive language'"Unison will be petitioning the next council meeting calling for the council leader to defend the rights of disabled people not to be abused in this way and for action to be taken over Councillor Fareham's disgraceful behaviour towards members of the public and trade union members."
Mr Fareham was reprimanded by the Lib Dem-run council's standards committee last year for making derogatory remarks about other staff.
He was ordered to write a letter of apology and attend a training course.
A Mencap spokesman said: "Councillor Fareham has now apologised for using that language, both on Twitter and to Mencap.
"We campaign about the use of language offensive to people with a learning disability because we believe that it contributes to a culture where harassment and bullying of people with a learning disability is all too common."
