Cumbernauld and Motherwell college chiefs said they were saddened by a decision by Coatbridge College not to join the merger.
A joint statement from the boards said: "Cumbernauld and Motherwell will still proceed with a two-way merger.
"Both colleges are fully committed to working with all colleges within North Lanarkshire and have reaffirmed that the door will remain open. We are hopeful Coatbridge will come back to the table and the three-way merger can continue."
A Coatbridge statement blamed the rejection of its proposals to "strengthen the governance arrangements of the proposed merger" by the other colleges.
A statement said: "Far from the door being open as was suggested, the college is being specifically excluded from the mainstream merger processes.
"The board regret they really have no choice but to withdraw from merger discussions."