The head of the letter carriers union says it’s a “disastrous idea.”

Fredric Rolando is reacting to the announcement that Saturday mail delivery will come to an end in August. Under the plan — aimed at saving up to $2 billion a year — mail would go to homes and businesses from Monday through Friday. Packages would still be delivered on Saturday.

Rolando says the move will hurt “millions of customers” — particularly businesses, rural communities, the elderly, the disabled and others who depend on Saturday delivery. He also says it goes against the will of Congress as expressed over the past 30 years.

But the postmaster general, Patrick Donahoe, says research indicates that nearly 7 in 10 Americans support the switch to five-day delivery as a way for the Postal Service to reduce costs.

It’s not clear how the service will be able to eliminate Saturday mail without congressional approval. Over the past several years, the Postal Service has advocated shifting to a five-day delivery schedule for mail and packages, and it unsuccessfully appealed to Congress to approve the move. The postal service gets no tax dollars for its day-to-day operations, but it is still subject to congressional control.