Two major unions representing employees at the U.S. Postal Service have reached a stalemate in negotiations with the agency, leading the parties to agree to continue the status quo.

The National Association of Letter Carriers and the National Postal Mail Handlers Union’s collective bargaining agreement -- in place since 2013 but retroactive to 2011 -- was set to expire on May 20, but both unions agreed with the Postal Service to extend it. The last NALC agreement, settled through arbitration, allowed for an extension “for successive annual periods” after the deadline unless “either party desires to terminate or modify it.”

The unions spent 90 days bargaining with USPS before deciding to extend the talks and keep the 2011-2016 CBA in place.

NALC President Fredric Rolando called the talks to date “productive and professional,” adding there “has been tangible progress on both sides.” Still, he said he could not “say definitively that we will be able to reach an agreement without resorting to” arbitration procedures.

Among the outstanding issues, he said, was boosting the wages for city carrier assistants, who serve as full time alternates to regular letter carriers. CCAs are not career employees -- meaning they do not receive the same pay and benefits as most USPS workers -- but have the opportunity to make that transition, if they are in good standing, as vacancies arise. Rolando said the new collective bargaining agreement should improve that conversion process.

He also promised to address the “work culture” at postal facilities, calling it a “major focus” of the talks. While Rolando acknowledged the union is negotiating in a time of “great challenges” for the Postal Service, he was clear that would not incentivize him to back down.

“The Postal Service must evolve to become an indispensable public utility for the internet age, and it is NALC’s responsibility at the bargaining table to shape that evolution constructively,” he said, “both to improve service and to assure the Postal Service’s long-term viability, while strengthening the terms and conditions of America’s city letter carriers.”

NPMHU also said both sides made “considerable progress” in negotiations, saying it agreed to extend the deadline so the items on which the parties had agreed would not be voided. Paul Hogrogian, the union’s president, told local leaders on Tuesday he was optimistic NPMHU and postal management would reach an agreement and avoid arbitration.

The Postal Service did not respond to inquiries into details on the negotiations, saying only in a statement it had agreed to extend the talks.

NALC represents 210,000 employees, while NPMHU represents 47,000 workers. Both unions are affiliated with the American Federation of Labor and Congress of Industrial Organizations (AFL-CIO).

The American Postal Workers Union, which has 200,000 members, is currently in arbitration with USPS to reach a new labor contract, with a final ruling expected in the coming weeks.