Sinn Féin president Gerry Adams is seeking an injunction against the BBC to force it to remove its Spotlight programme from its website.
A plenary summons, issued to commence the case against the broadcaster, was lodged on Friday at the High Court in Dublin.
The Louth TD had already initiated defamation proceedings against the broadcaster in March.
The action followed allegations in the Spotlight programme, broadcast last September, that Mr Adams sanctioned the 2006 murder of former senior party official and British agent Denis Donaldson. Mr Adams has denied the claim.
A link to the programme is still available on the BBC’s website.
Mr Donaldson was shot dead near Glenties in Co Donegal in April 2006, after he confessed to being a British agent, having worked for MI5 for 20 years.
The revelation directly led to the collapse of Stormont’s institutions. No one has been prosecuted for his killing, which was claimed three years later by the Real IRA.
Testimony
The Spotlight programme based its claim on testimony provided by another British agent called “Martin” who had infiltrated the Provisional republican movement.
“I know from my experience in the IRA that murders have to be approved by the leadership,” he told Spotlight. Specifically asked to identify who ordered the killing, he said: “Gerry Adams, he gives the final say.”
After the programme aired, Mr Adams described the allegation as “nonsense” and said he intended to sue the BBC.
“I have been consulting with my lawyers and we will now be taking action against the BBC in relation to this totally false allegation contained within the BBC Spotlight broadcast,” he said.
An ex-Real IRA leader also publicly insisted his former organisation, and not the Provisional IRA, murdered Mr Donaldson, after the programme was aired.
Public interest
The BBC said, at the time, that the Spotlight programme dealt with matters of great public interest and it would stand by its journalism.
Mr Adams is represented by high-profile defamation solicitor Paul Tweed, of Johnsons Solicitors.
Mr Tweed told The Irish Times the fresh plenary summons was issued to cover the BBC’s “failure to remove the online publication”, and reliefs sought included an injunction to have the programme removed.
Asked why the action was taken in Dublin, Mr Tweed said the claim for damages is limited to Mr Adams’s reputation in Ireland.
“Obviously he is a TD elected in Dundalk so that’s the reason for that,” he said.
Asked whether Mr Adams would opt to have his case put to a jury, should it go to full hearing, Mr Tweed said most of his clients do elect for a jury hearing.
