Washington (CNN) -- After a nearly six-week voting process, it's going to take a little longer before the Transportation Security Administration knows which union will represent its 40,000-plus airport screeners.
The process, with the goal of deciding if the screeners will have limited union rights, ended Tuesday.
"Today the Federal Labor Relations Authority (FLRA) released the unofficial results of the union election at TSA. No ballot option received a majority of votes, meaning that a runoff election is necessary between AFGE and NTEU," agency Administrator John Pistole said in a statement released after the results were made public.
The American Federation of Government Employees received more votes than the National Treasury Employees Union, but not a majority in the election for exclusive union representation of the transportation security officers. AFGE received 8,369 votes and NTEU 8,095. Workers cast 3,111 votes to reject a union.
Federal Labor Relations Authority election rules require a runoff when there is no majority.
Earlier this year, Pistole granted transportation security officers the ability to vote on whether they wanted to be represented by a union for purposes of engaging in limited, clearly defined collective bargaining on non-security-related employment issues. Bargaining on any issues related to security would be strictly prohibited.
AFGE National President John Gage, in a statement issued after the vote was announced, said, "During a time when this country's federal workers and their unions are under attack, it speaks volumes that transportation security officers nationwide stood strong and voted to have a union.
"By voting for a voice at work, TSOs have demonstrated that when American workers are given a choice -- without intensive intimidation campaigns -- they want a union. While AFGE is disappointed that we can't begin negotiating a collective bargaining agreement right away, we are confident that TSOs will once and for all vote for AFGE in a runoff election."
NTEU President Colleen Kelley released statement saying, "NTEU is prepared for a runoff and will continue its assertive nationwide campaign among TSA officers."
She expressed confidence her union will win the runoff. "NTEU is widely known and highly respected for having the best on-the-ground representation and negotiating the best contracts in the federal sector," she said.
Pistole added, "The safety of the traveling public remains our top priority and I have made clear we will not negotiate on security. However, I continue to believe that employee engagement and morale cannot be separated from achieving superior security.
"No matter which union ultimately prevails, we hope and expect that they will join us to further improve TSA's performance of its critical security mission and support our frontline officers as they carry out this mission."
When Congress created the TSA in 2003, it gave the administrator the authority to decide whether screeners should be allowed to engage in collective bargaining. Bush administration TSA chiefs opted not to endorse bargaining, saying it would impede their ability to protect the public. But Pistole announced he would allow airport screeners to select a union for collective bargaining.
Runoff election dates have not yet been set.
CNN's Jeanne Meserve and Mike Ahlers contributed to this report.