One of the partners in the Plant Vogtle nuclear plant expansion said Monday that it doubts that the much-delayed project will be completed by its latest deadline.

The latest completion deadlines of December 2019 and September 2020 for the two new reactors — already more than three years behind schedule — "do not appear to be achievable," Oglethorpe Power Co. said in a filing to the U.S. Securities and Exchange Commission. The latest deadlines had been supplied by the project's construction contractor, Westinghouse, in February, Oglethorpe said in its filing.

The Obama Administration backed new federal loans for a nuclear project in Georgia.

Such delays are the biggest source of cost overruns at the Vogtle expansion, which is more than $3 billion over budget.

Atlanta-based Georgia Power is the lead partner and owns nearly half of the project to build two new nuclear reactors at its existing Plant Vogtle complex near Augusta. Oglethorpe owns 30 percent and a handful of other partners own the remainder.

Oglethorpe's warning of more costly delays comes as storm clouds were rolling over the Vogtle project's key contractor, Westinghouse, which could seek bankruptcy protection from creditors as soon as Tuesday, according to press reports.

Citing an unnamed source, Reuters reporters in Tokyo reported Monday that Westinghouse's parent company, Toshiba Corp., wants its U.S. nuclear unit to file Chapter 11 as soon as Tuesday.

A bankruptcy filing by Westinghouse would be aimed at limiting Toshiba’s financial damage from more than $6 billion in losses on the Vogtle project and a similar project in South Carolina.

Critics of the Vogtle project have said a bankruptcy filing would likely lead to more delays. It could also allow Westinghouse to renegotiate the construction contracts under the bankruptcy court’s supervision. That could ultimately lead to higher costs for Georgia Power, its partners, and their customers if state regulators approved.

As it is, Georgia Power will be cutting it close to get the new nuclear plants completed ahead of a deadline contained in a deal it reached last year with state regulators.

Under that settlement with the Georgia Public Service Commission, the Atlanta electric utility must have the plants in running condition by the end of 2020, or its profit margin allowed on the project will be cut by roughly a third.