Postage rates jumped Sunday for the first time in two and a half years as the U.S. Postal Service hopes to generate more revenue amid historic losses.

First-class postage stamps now cost 45 cents each, a price jump that officials anticipate will generate an additional $888 million in annual revenue. The rate increase does not affect the use of Forever stamps purchased before Sunday.

The price hike comes as negotiations between the U.S. Postal Service and two of its labor unions reached an impasse that may require a ruling by an arbitrator.

Postal and union officials announced late Friday that separate talks had collapsed between the USPS and the National Association of Letter Carriers and the National Postal Mail Handlers Union. Contracts with both unions, which represent a combined 242,000 postal workers, expired in late November. Negotiations were extended twice before failing Friday.

Under the rules of postal labor negotiations, the parties may next engage in talks with a mediator if both sides agree. The mediation process generally lasts about two months, the USPS said. If those talks fail, both sides would likely turn to a third-party mediator, who would determine the final details of a new labor agreement. By law, arbitrators are not required to consider the Postal Service’s financial condition when making a final ruling.

Federal law prohibits postal workers from striking during a labor impasse.

The NPMHU — which represents mostly backroom mail handlers — thanked its members Friday for their continued patience.

NALC President Fredric Rolando said Friday that his union’s negotiations had been “innovative, professional and productive,” adding that “a negotiated agreement is in the best interests of the parties, the businesses that rely on us and the nation we serve.”

NALC hired former Obama administration car czar Ron Bloom in October to advise the union on negotiations and to develop new business proposals for the USPS. Those proposals have not been released.