As reported in the Gazette last week, the branch is earmarked for closure as part of a review of the post office network.
Coun Forbes Grant told North Sunderland Parish Council: "I'm very much against the closure of North Sunderland post office. The village is expanding and the branch is not only used by people in North Sunderland but a considerable amount of people in Seahouses.
"We should write a letter to the council expressing our regret that they plan to close the post office at North Sunderland.
"I've got to say there is an awful lot of people who won't use the Seahouses post office."
Coun Jane Winter said: "It is the only facility in North Sunderland and for many people the only way of going down to Seahouses is on the infrequent bus service.
"North Sunderland as a village is growing."
Longframlington and North Broomhill are also set to close while other branches are to be replaced by an outreach service.
Meanwhile Northumberland County Council's executive this week pledged to support communities through possible Post Office closures.
Coun Jeff Reid, council leader, said: "This is an important issue for a number of Northumberland communities, particularly as one of the most sparsely populated counties in the country.
"We must seriously consider what happens to the communities if the branches are closed, since post offices are often a very important part of a viable community.
"The timetable for responses to the consultation and for researching and producing proposals for alternatives is very short. It is essential that we work with other councils to see what can be done and to decide on next steps.
"We are urging colleagues in parish and district communities to join us in discussing the consultation in an early meeting that we have already secured with Royal Mail.
"We will help communities however we can, and look forward to discussions with Royal Mail and other partners.
"We are determined to maintain and improve the vitality of all Northumberland, rural and urban."
A consultation meeting between the Post Office, the county council and district and parish councils is to take place at County Hall tomorrow.
The public consultation lasts until Monday, August 11.