The Martha’s Vineyard airport commission has the authority to establish salaries for its employees independently of other county employees salaries, an attorney for the Dukes County commission said.

In a letter sent by email to county manager Martina Thornton on Dec. 11, Darren Klein, an attorney with Kopelman and Paige wrote: “In my opinion, as long as the airport commission has sufficient funds appropriated through the enterprise fund or otherwise, the airport commission has the authority . . . to fix salaries as it sees fit.”

Last month the county manager raised the issue of different pay increases for county and airport employees. In a memorandum to the county commission on Nov. 14, Ms. Thornton noted that four airport nonunion employees received a 3.1 per cent cost of living adjustment while county employees received a 1.28 per cent adjustment. The adjustments took effect July 1 at the start of the 2013 fiscal year.

“This situation points to unfair labor practice and the county employees would like to know why this is allowed,” Ms. Thornton wrote.

County commissioners voted to seek a legal opinion on the matter.

In his letter Mr. Klein said under Massachusetts General Laws, the airport commission can fix salaries and increases for officers and employees even if they are different from other county salaries.

“In fact, including airport employees on a county pay scale would arguably violate the provisions of [state law],” he wrote. “Moreover, it is not an unfair labor practice, in my opinion, to give out different raises to different employees, especially when those employees fall under the authority of the airport commission rather than the county commissioners.”