Delta Air Lines Inc. now faces a second investigation over its handling of another union election.
The federal National Mediation Board told the airline on Monday that it would take a closer look at whether elections for three groups of workers were tainted. Last week, the NMB said it would do the same thing regarding a vote late last year that was narrowly lost by the Association of Flight Attendants-CWA.
Pilots were the only large unionized group at Delta when it bought Northwest Airlines in 2008. The purchase triggered elections to see whether the unions who had represented Northwest workers would represent the combined groups.
Three votes covering about 29,000 workers ran through November and December. The union complained Delta improperly interfered.