The Ulster Unionist Council has pledged to take "further action" following the apparent discovery of a list of senior Conservatives in IRA intelligence files.
The document was seized during searches following a break-in at Special Branch offices in Belfast blamed on republicans. The document was not, however, one of those taken in the that break-in. Republican sources have strenuously denied involvement, pointing to British security services as possible culprits.
Ulster Unionist MP Mr Jeffrey Donaldson said: "The IRA cannot have it both ways.
"If they think the Ulster Unionist Party is going to sit back and ignore their activities they can think again."
A meeting of the Ulster Unionist Council's ruling executive last night unanimously passed a motion take the matter further.
Although tactics have yet to be finalised, party leader and Northern Ireland First Minister Mr David Trimble, who flew back to the North last night, is now expected to press for sanctions against Sinn Féin.
This could involve demanding the party's exclusion from Northern Ireland's power sharing government.
Both the acting chief constable, Mr Colin Cramphorn, and Northern Ireland Secretary Dr John Reid insisted there was no information to suggest the IRA was on the verge of a new campaign of violence.
Sinn Féin claimed it was the latest attempt by security forces to falsely accuse republicans of last month's burglary at the Castlereagh complex in east Belfast when top-secret Special Branch files were stolen. PA