Staff at BP's Grangemouth plant face an uncertain future after the oil giant announced plans to sell off part of the business, unions have warned.
About 500 people are employed in the division at Grangemouth
The company intends to offload half of its petrochemicals business, which employs about 500 people at the plant.
Its Olefins and Derivatives (O&D) division will be turned into a separate company which will either be sold or floated on the stock market next year.
The Transport and General Workers' Union said the decision was a shock.
Regional industrial organiser Pat Rafferty said: "Workers at BP Grangemouth face an uncertain future.
"They have worked hard to accommodate restructuring and feel that they have been rewarded for their co-operation by being transferred out of the company.
"Our experience of employment transfers shows that workers often end up worse off under the new employer."
Unions are seeking guarantees about long-term job security and want the new employer to match the BP pension scheme.
"The BP Group is making substantial profits yet they don't seem enough to satisfy the board," added Mr Rafferty.
"This decision has come from the top with little thought for the workers and it smacks of corporate greed."
However, BP said it hoped the decision would be best for all concerned.
The division has had to compete against more profitable parts of the company for investment, and BP hopes the new owner will be committed to its future.
Chief executive Lord Browne said the move was also "likely to deliver the best returns for shareholders".
The O&D division makes products used in
plastic goods such as food and drink containers and automotive parts.
It employs more than 7,000 people across the world, including Germany and the US, and has about £3.64bn of the petrochemicals business' operating capital.
Iain Conn, the current chief executive of BP Petrochemicals, said: "Our O&D sub-segment is one of the highest-quality portfolios of its kind in the petrochemicals industry.
"It has a global network of manufacturing sites, good technology, a fine range of products and strong market positions.
"As a free-standing entity it will be a significant competitor in its sector."
Cathy Peattie MSP, whose Falkirk East constituency includes the refinery, said she would raise the sell-off issue in the Scottish Parliament.
She added: "A great deal of uncertainty surrounds the plan for O&D to become a separate company.
"This could have major consequences, not only for Grangemouth and surrounding areas, but for Scotland as a whole. I'm sure the Scottish Executive will be very concerned about this development."
And Liberal Democrat MSP Donald Gorrie called on BP to ensure the protection of jobs at its Grangemouth plant.
The Central Scotland member said: "This sell-off must not become a disaster
for the 500 workers at the company's plant. They have been more than co-operative over recent restructuring."