The DUP has lodged an objection to plans for a waste incinerator near the site of the Battle of the Boyne.
Jim Wells, the party's environment spokesman and a South Down Assembly member, lodged his objection with Meath Co Council on Wednesday. It is the first time the leading unionist party has concerned itself with a major planning issue in the Republic.
The objection relates to a new planning application for Belgian multinational Indaver to construct a waste incinerator near the battle site and close to the Unesco world heritage site of Brú na Bóinne, which includes Newgrange.
The Orange Order and the Independent Loyal Orange Institution has called on Unesco to expand its world heritage site to include the Boyne battlefield, believing the site to be of central importance to European history and political development, a move which the DUP supports.
Mr Wells said last night he had been invited to join objectors in Co Meath and was happy to support them because the issue had important direct links with Northern Ireland.
The Battle of the Boyne site, like the Somme, was of particular relevance to unionists, Mr Wells told The Irish Times last night.
"I'm also concerned about the question of emissions in neighbouring constituencies," he said.
The Republic's authorities "ought to preserve landscape rather than trying to industrialise it," he added.
Mr Wells denied he was interfering in the affairs of another state: "The difference is I was invited," he said. "I didn't search for this, they invited me. We are not meddling.
"The final decision rests with Meath County Council and Irish authorities - they have the right to make their own decisions."
A representative for Indaver claimed last night that Unesco reported last year that earlier plans for an incinerator would not degrade its heritage site.
The company hopes to complete the planning process by the end of this year. If successful, construction would begin in 2007 and take two years to complete.