The Postal Service said in February it planned to keep Saturday deliveries of packages but cut Saturday mail delivery to save billions of dollars.
But to do so, Congress would have had to drop the mandate. Instead, it was kept going in a funding bill that passed in March, CNNMoney reported.
"Although disappointed with this congressional action, the board will follow the law and has directed the Postal Service to delay implementation of its new delivery schedule until legislation is passed that provides the Postal Service with the authority to implement a financially appropriate and responsible delivery schedule," the agency's ruling board said in a statement.
Rep. Darrell Issa, R-Calif., said he was "disappointed," with the decision.
"It is quite clear that special interest lobbying and intense political pressure played a much greater role in the Postal Service's change of heart than any real or perceived barrier to implementing what had been announced," said Issa, the chairman of the House Oversight Committee.