The Dundonald Ulster Bank was one of 10 across Northern Ireland the company announced would close, although no compulsory staff redundancies are expected.
Alliance MP Mrs Long said the move was a blow to the Dundonald area.
“It is a disappointing move by Ulster Bank, especially considering Dundonald is a vibrant, growing community. Ulster Bank have stated the move is due to an increasing number of customers doing their banking online. But this attitude dismisses many residents of Dundonald, particularly older ones, who prefer to use the bank in person.
“While the fact that no job losses are expected is to be welcomed, I will press Ulster Bank to ensure they keep at least an operational ATM in Dundonald, so residents there can continue to have access to at least some services.”