WASHINGTON (AP) — The new spending bill passed by Congress on Thursday appears to continue the requirement for six-day mail delivery, but some lawmakers and postal officials say plans to cut Saturday service should proceed.

The financially troubled Postal Service announced last month that it would switch in August to five-day service for first-class mail and continue six-day package delivery. The government at the time was running on a temporary spending measure and postal officials invited lawmakers to spell out the way ahead in the 2013 spending bill. That sweeping funding bill was approved Thursday without new language.

Some lawmakers say a longstanding provision in the bill mandates six-day delivery. Postal authorities argue they still will have delivery over six days, just that not all mail will be delivered all six days.

Meanwhile, the Government Accountability Office weighed in with an opinion that the postal agency did not have the right to unilaterally end Saturday mail.

“We strongly disagree with the GAO’s legal opinion,” said David Partenheimer, spokesman for the Postal Service.

“The critical issue is that the Postal Service is losing $25 million per day under its existing regulatory structure.”

The letter carriers union, which has strongly disagreed with the Saturday cutback plan, sided with the GAO.

“We fully expect the Postal Service’s board of governors and the postmaster general to follow the law and the expressed will of Congress about maintaining six-day delivery,” Fredric Rolando, president of the National Association of Letter Carriers, said in a statement. “We do not expect to have a legal fight.”