The MSP for Galloway and West Dumfries has described P&O Ferries' redundancies as "awful news".
He wrote: "Awful news as P&O sacks 800 workers apparently without any notice.
"I will be doing what I can to support those [affected] & seeking answers from P&O and again ask @ScotGovFM and @UKGovScotland to do what they can to protect crew and services."
P&O Ferries made the announcement earlier today, putting the decision down to the company losing £100 million year on year.
Staff are going to be replaced by agency workers, with ferry sailings being suspended "for the next few days".
In a statement, released on Thursday afternoon, they said: "P&O Ferries plays a critical role in keeping trade flowing, supply chains moving, and connecting families and friends across the North and Irish seas and the English Channel.
"We have been at the heart of this service for years and we are committed to serving these vital routes.
"However, in its current state, P&O Ferries is not a viable business. We have made a £100m loss year on year, which has been covered by our parent DP World. This is not sustainable.
"Our survival is dependent on making swift and significant changes now. Without these changes there is no future for P&O Ferries.
"These circumstances have resulted in a very difficult but necessary decision, which was only taken after seriously considering all the available options.
"As part of the process we are starting today, we are providing 800 seafarers with immediate severance notices and will be compensating them for this lack of advance notice with enhanced compensation packages.
"In making this tough decision, we are securing the future viability of our business which employs an additional 2,200 people and supports billions in trade in and out of the UK.
"And we are ensuring that we can continue serving our customers in a way that they have demanded from us for many years."