The International Association of Machinists and Aerospace Workers said on Friday that it withdrew its application to hold a representation election for fleet service workers at Delta Air Lines Inc, a move the U.S. carrier called repugnant.

In August, the machinists union asked the National Mediation Board to declare that Delta and its Northwest Airlines subsidiary operate as a single carrier with respect to fleet service, flight simulator technician and plant protection worker groups. The filing with the NMB is a step in the process leading to a union representation election.

The machinists union said in a statement that it withdrew its filing with the National Mediation Board on behalf of fleet service employees because of Delta's insistence that representation for those workers be resolved at the same time as it is for passenger service and office and clerical employees.

The machinists union has not yet sought union elections for those two groups.

Delta, which was largely non-union before acquiring Northwest last year, said the machinists union's withdrawal of its application for fleet service workers was the continuation of a pattern of stalling resolution of union representation for its employees.

The timing of the IAM's action is suspicious considering it is taking place days before the NMB publishes its proposal to change the longstanding majority voting rules, Delta added in a statement.

Atlanta-based Delta was referring to an expected response by the mediation board to a request by the U.S. AFL-CIO labor federation for a rule change that would base the outcome of union elections at airlines on the majority approval of people who vote.

Currently, union elections at airlines and rail companies covered by the decades-old U.S. Railway Labor Act are decided by a majority of an entire workgroup. In practice, that means members of a worker group who don't vote are effectively counted as 'no' votes.

U.S. airline groups oppose the rule change.

(Reporting by Karen Jacobs)