Delta Air Lines has refused a demand by its pilots union for a voting seat on the board of directors, which could affect plans for a joint venture between Delta and United Airlines.

The union made the demand as a prerequisite to a contract change needed to allow the airline alliance, in which Delta and United would sell seats on each others' flights in a practice called code-sharing.But Atlanta-based Delta said Monday its board rejected the demand "because of its belief in the principle that an independent board best serves Delta and its constituents."