The flight attendants’ union for American Airlines says it plans to add pressure on the company following a decision by an independent federal agency to deny the union’s request to strike.

The National Mediation Board (NMB) on Tuesday denied a request from the Association of Professional Flight Attendants (APFA) to be released from federal mediation, according to a news release from APFA, which represents American Airlines’ roughly 27,000 flight attendants.

“As of today, the National Mediation Board … has denied our request for release into a 30-day cooling-off period,” said APFA president Julie Hedrick in a statement, per NBC 5 DFW.

“Flight Attendants at American Airlines are working under wages negotiated in 2014 while management continues to drag out bargaining with contract proposals that do not address the current economic environment.”

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The APFA said it strongly disagrees with the NMB’s decision and will continue to intensify pressure on American Airlines until a deal is reached. In total, the APFA has been in contract negotiations with American Airlines for nearly five years without reaching a comprehensive agreement that is acceptable to both sides.

“We have a right to strike under the Railway Labor Act,” the organization said in a news release. “For far too long, airline management has exploited workers, funneling profits into their own pockets. The Railway Labor Act was meant to protect us, the workforce, yet it’s been twisted into a tool for corporate greed.”

The Railway Labor Act’s purpose is to “avoid any interruption of interstate commerce by providing for the prompt disposition of disputes between carriers and their employees and protects the right of employees to organize and bargain collectively.”

According to APFA, American Airlines received the union’s economic proposal in March but has refused to respond to any counter proposals since September.

“They have been stonewalling us, offering nothing but a single, rigid economic framework that does not address our current economic needs. This is not negotiations; it is a mockery of our efforts,” the union said.

In response to the NMB’s decision, the Fort Worth-based airline released the following statement.

“We look forward to continued negotiations with APFA and reaching an agreement our flight attendants have earned,” said American Airlines, per NBC 5.