Newcastle College is considering merging with two other colleges, both rated inadequate by Ofsted, and each more than a hundred miles away.
The proposal follows pleas from Keighley College and Skelmersdale and Ormskirk College for merger partners. It would mean forming one institution with campuses based up to 160 miles apart.
Jackie Fisher, Newcastle College principal, told union officials that they had drawn up a plan which would allow the two colleges to maintain independence within one college framework.
But the University and College Union said it doubted that a college merger would work across hundreds of miles, and said it hoped Newcastle College's management style would not spread.
Barry Lovejoy, the union's head of colleges, said: "We are not against mergers per se but have serious doubts about these proposals - partly because of the huge distances involved and partly because of Newcastle College's very sorry recent record on industrial relations.
"We also question how these colleges could keep their local identity and community involvement in a merger with a college so far away."
Newcastle was involved in a protracted dispute with lecturing staff over forced changes to their contracts, which led to seven walk-outs in six months.
"The last thing either Skelmersdale or Keighley College need at the moment is an uncertain industrial relations climate which will further lower staff morale and so damage the quality of teaching and learning," Mr Lovejoy said.
Newcastle declined to comment about the potential merger, although the college defended its record on staff relations, saying a staff survey last year reported high levels of satisfaction at work.
As well as the Newcastle proposal, Keighley College is considering bids from at least 10 other colleges, while Skelmersdale and Ormskirk College has received four expressions of interest.
Both declined to comment on any bids while they were still under consideration.