Another group of Delta Air Lines employees will remain non-union after a federal board on Monday upheld the results of voting by stock clerks against unionization.

The National Mediation Board, which governs labor relations at airlines, dismissed the International Association of Machinists union's claims that the company had inappropriately interfered in the representation election.

Employees from Atlanta-based Delta and its merger partner Northwest voted in a series of elections last year to determine whether to be unionized or not under the combined Delta. In the Delta stock clerks election last year, 439 voted for no union, while 168 voted for representation. The Mediation Board found that conditions for a fair election were not tainted.

Delta flight attendants were the first group to learn they would remain non-union when the Mediation Board upheld the election results earlier this month. The Mediation Board has not yet released decisions on interference claims in the elections among Delta customer service employees and baggage handlers represented by the Machinists union.