The U.S. Postal Service pushed back a plan to award an expected $6 billion in contracts for the next-generation mail truck later this year.

In a filing, the agency said it moved the deadline for four separate company teams to provide contract proposals to build the new truck until July 14. The proposals were originally due on March 27. Each of the teams previously has provided prototype vehicles to the Postal Service for evaluation.

The document did not outline why the deadline moved. The USPS has provided very few details about the status of its program to replace aging mail trucks.

The Postal Service has previously said the contract could be more than $6 billion of business to build as many as 180,000 delivery vans. It also has said the contract could be split between multiple parties and that the mail truck needed to be assembled in the U.S.

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