Former SDLP leader John Hume challenged his senior colleagues about privately "consorting" with Fianna Fail TDs as he battled to secure his leadership, it has emerged.
State files show a senior Foreign Affairs official was briefed by Mr Hume about tensions between senior party members after ex-leader Gerry Fitt resigned in 1979.
In December that year, just after Mr Hume was elected head of the SDLP, he told his Irish government contact he had confronted both Seamus Mallon and Paddy Duffy.
"Part of Mr Hume's concerns at present seems to be the restriction of Seamus Mallon's role," the official wrote. "He referred again to contacts which Mallon was said to have had with certain members of the Fianna Fail party who are rumoured to hold views on Northern Ireland policy differing from those of the government.
"Hume said he had challenged Mallon about this and received an assurance that the only contact of that nature had been in the form of a visit Mallon had received when sick in hospital in Dublin."
The file shows that Mr Hume had also confronted Paddy Duffy about reports he was "consorting" with Neil Blaney. "Duffy had given a complete denial," the official wrote.
"His relationship with Mallon is unlikely to be an easy one given the latter's insatiable ambition," he added. "Opportunities will not be rare for Mallon to manoeuvre given Hume's frequent spells of absence in Europe."
Mr Hume said he was determined to keep tighter control over the party than his predecessor and claimed to have secured reconciliation within the party and loyalty to him.
Earlier that day he had met Austin Currie and they had laid to rest past differences.
The then SDLP leader said Mr Fitt would be missed, if only in an organisational sense, and that he was not looking forward to the task of leading the party from his European Parliament base.