Jeremy Corbyn is taking legal action over a doctored image used in a tweet about the recent Liverpool terror attack.
Paul Nickerson, a Conservative councillor, posted the doctored image showing the ex-Labour leader holding a wreath near a burning taxi.
The East Riding of Yorkshire councillor since deleted the tweet and apologised, but denied he was responsible for the posting of the image.
Mr Corbyn has said: "My solicitor has been notified and we are taking legal action."
The tweet contained the image and the caption: "Unsurprisingly".
It is thought the image was a reference to a row which erupted when pictures of Mr Corbyn attending a wreath-laying ceremony at a Tunisian cemetery surfaced.
Mr Nickerson, ward member for Minster and Woodmansey on East Riding of Yorkshire Council, was suspended by the council's Conservative group and has faced calls to stand down.
He has since written to Mr Corbyn, the MP for North Islington, to apologise.
In his email to Mr Corbyn, he said he took full responsibility for the tweet and the distress it caused, but maintained others had sent it.
He added he was also aware that it had caused particular offence in Liverpool, both due to the attack and local respect for the former Labour leader.
Mr Nickerson wrote: "I recognise that as a politician you will be open to many lines of criticism but I feel this fell below the high standards others and especially you personally have demonstrated in your own communications.
"You have worked tirelessly not just for your own constituency but for many in Liverpool and as an advocate of the people of Liverpool they have rightly been upset and offended by this."
East Riding Council leader, Conservative councillor Jonathan Owen, said offensive messages from members, no matter the intention, would not be tolerated.
He added an investigation was now under way and that people expected councillors to behave appropriately at all times.
Speaking on Wednesday, Mr Nickerson said he felt his suspension was reasonable while an investigation was conducted and pledged to co-operate fully.