The management team interested in buying Tata Steel has raised the prospect of cutting 1,000 jobs if it is successful.
Excalibur Steel UK Limited said its proposals were founded on an approach that "re-engineers" the existing organisational arrangements.
Unions expressed concern about jobs being cut at Tata plants, including the country's biggest steel plant at Port Talbot in south Wales.
There have been two expressions of interest to buy Tata Steel, from the management team and Liberty House.
Excalibur said in a statement: "The opportunity for greater efficiency involves evolving from a highly functional centralised business model, with significant fixed costs and overheads.
"This arises because the existing arrangements are based on a pan-European structure.
"Excalibur's proposals will see a migration towards leaner autonomous sub-business units.
"In the event Excalibur is successful in acquiring Tata's UK steel assets this will inevitably take some time to achieve.
"Potentially this could affect up to 1,000 jobs across the entirety of the operation."
Roy Rickhuss, general secretary of the Community union said: "These are worrying reports for steelworkers, who are already facing uncertainty. We have had no discussions with Excalibur about additional job losses.
"We await to see the details of their plans for the business and any implications for jobs.
"However, this news is somewhat surprising given that their bid is based on the original turnaround plan, which included a restructuring of 1,050 jobs that is ongoing."
Unite assistant general secretary Tony Burke said: "Tata steelworkers at Port Talbot and across Tata sites in the UK make some of the best steel in the world.
"Our members' skills and experience are central in securing a successful future for the UK's steel industry and must be at the forefront of any potential bidder's plans.
"Protecting jobs in the UK steel industry and making steel here in the UK is the priority of our members.
"We will be seeking details directly from both Excalibur and Liberty House on their proposals over the coming days, including their plans for employment levels across the UK."