Fine Gael MEP Mr Gay Mitchell demanded an investigation tonight into the "sinister" disappearance of official constituency letters.
The Dublin TD said interference with Oireachtas mail was a serious matter.
"There's a prima facie case that my official post as a member of the Dail was interfered with at the point of delivery," he said.
"I don't know who's involved but if republicans were carrying out surveillance on TDs they have to be on the list of suspects."
Mr Mitchell acknowledged that it was not uncommon for mail to get lost in the post but said the disappearance of three letters clearly marked with the Oireachtas stamp was too coincidental.
"I have to say I suspect something sinister," he said. "Some person, identifying an envelope as an Oireachtas envelope, took it out of circulation.
"I don't know who they might be but in the context of the surveillance of TDs in recent days I have raised it in the Dail and would like the matter to be debated."
The incident emerged in February when in the space of 10 days the letters were signed and put into the usual Oireachtas postal system, all addressed to a small part of Mr Mitchell's Dublin South Central constituency.
The letters concerned personal issues relating to public authorities.
Officials at Leinster House are certain the mail left the building.
On April 1st Mr Mitchell wrote to the Ceann Comhairle calling for an investigation into the matter. Having received no reply he wrote again in June.
He said his constituents had the right to privacy and that constitutional and legal issues were involved.
The MEP, who was Fine Gael's foreign affairs spokesman at the time of the incident, has demanded the Committee of Procedures and Privileges investigate the matter.