Flight attendant union organizers at Delta Air Lines got a step closer Wednesday to a re-vote in the election they lost late last year.

The National Mediation Board sent a memo to Delta and the Association of Flight Attendants saying it will investigate union allegations that Delta illegally interfered in the election and thus tainted conditions for a fair vote.

The decision follows a review of filings by both parties. Now the Mediation Board will conduct an on-site investigation and interview employees. The process could take several months.

Delta flight attendants "will finally have their day in court," AFA president Veda Shook said in a written statement.

Delta spokeswoman Gina Laughlin said the company is "disappointed" in the decision and the delay it poses for the integration of pay, benefits, work rules and seniority for flight attendants from Delta and merger partner Northwest Airlines.

The election was conducted to determine whether the combined workforce from non-union Delta and unionized Northwest would be unionized. The division between the two sides at times led to nasty exchanges and discord among some flight attendants.

The memo from the Mediation Board, which governs union elections at airlines and railroads, noted that the union filed allegations of interference shortly after the election last November and that Delta also raised allegations about the union's conduct during the election.

The Mediation Board is still reviewing a similar appeal by the International Association of Machinists union, which lost representation elections at Delta last year.