The spectre of sale or closure has been hanging over Kvaerner Energy's Clydebank operations since it was revealed in December that a management buy-out attempt had failed.
A consortium including some former managers has put together a deal which union leaders hope will safeguard many of the 250 jobs at the former John Brown Engineering plant.
But Kvaerner said that more than 100 jobs could actually be lost in the short-term if the deal with Newco went ahead.
A company spokesman said that the agreement reached on Friday with Newco - the working name for the consortium - was a "letter of intent" to sell the plant.
The spectre of sale or closure has been hanging over Kvaerner Energy's Clydebank operations since it was revealed in December that a management buy-out attempt had failed.
Work is due to run out in the autumn and Kvaerner has warned of redundancies.
In May, workers staged a "work-in" at the plant to protest at proposals to sell the company to Manchester firm Texas.
Manual workers barred senior management from entering the main factory.
Kvaerner Energy is part of the Kvaerner Thermal Power Group, which includes operations in Norway and the Middle East.
The company designs and builds power stations and supplies and services heavy duty gas turbines worldwide.