The main contractor carrying out works on Lews Castle is experiencing cash flow problems which have now impacted on a local sub-contractor.
Northern Irish company, Patton, are carrying out the £2m programme of repair works to the building funded by the Comhairle, Historic Scotland and the Heritage Lottery Fund.
A spokesman for Patton said the business was not in administration but was facing cash pressures as a result of the recent downturn in the construction sector.
He added: “We have been working with our bank over recent months to seek to navigate our way through what has been and continues to be a very difficult period. This contact is ongoing.”
Comhairle nan Eilean Siar say they are monitoring the situation.the Castle.