Paul Murphy has accused the Taoiseach of defaming him - and is to make an official complaint to the Dáil authorities.
He says Leo Varadkar accused him of criminal behaviour in the Dáil on Wednesday - and is also complaining about four other Fine Gael TDs.
The claims come in a letter to be delivered to the Leinster House authorities today.
Our political correspondent Gavan Reilly has seen an early draft:
