USPS announced in May that it would start consolidating processing facilities over the summer, with a second phase beginning in early 2014. The fully implemented consolidation plan would affect 229 plants in all.
A spokeswoman for the Postal Service said Friday afternoon that the agency was reviewing the PRC opinion, but was not yet able to comment.
In its opinion, the PRC also said that the Postal Service had rejected much of its own modeling on which plants should be consolidated, and said that the agency needed to seek out more information on what changing its proposed delivery changes might need.
The regulator, in calling out USPS for being too rosy with its assumptions, also said that the Postal Service would need to improve its overall productivity by 20 percent for its projections to come true.
“The commission cautions that improvements of this magnitude are remarkably ambitious and involve some risk,” the opinion said.
Over the summer, the Postal Regulatory Commission rejected a request from the American Postal Workers Union to stop the Postal Service from moving ahead with the consolidation efforts.
The PRC has also questioned the Postal Service’s push to scrap Saturday delivery and to close post offices, an idea USPS has now backed away from.