DETROIT – General Motors Corp. plans to idle most its plants for about two months this summer as the company races to cut costs and production to keep pace with sinking demand, said a person familiar with the plan.

The car maker typically closes its plants for a two-week summer vacation. A GM spokeswoman declined to confirm or deny the planned closure, The Wall Street Journal reported.

Such a production hiatus — one of GM’s longest in recent decades — promises to drain the company’s revenue stream, dealing another blow to its attempt to restructure operations. GM’s sales have tumbled in recent months, with declines topping 50 percent.

United Auto Workers union members still receive most of their pay during such shutdowns.

GM is saddled with a 113-day supply of cars and a 123-day supply of trucks sitting unsold on dealer lots as of March 31, according to Ward’s Automotive Reports.

The car maker closed its plants for over a month starting with Christmas week this winter.

Also Wednesday, GM’s No. 2 executive toughened the company’s message to bondholders, saying it doesn’t plan to pay off $1 billion in debt due June 1 and instead will rely on an exchange for shares or bankruptcy-court protection to clear its balance sheet.

Chief Financial Officer Ray Young, speaking to reporters on the sideline of a conference near Detroit, said the move comes even as the auto maker is finalizing details with the Treasury Department to receive an additional $5 billion in loans.

By taking a tougher public stance on bondholders, GM executives are laying the groundwork for what promises to be a messy debt-for-equity offer that they expect to launch by next week. The car maker will offer to exchange $28 billion in unsecured debt for company stock that could be rendered worthless without a significant turnaround.

GM faces a June 1 deadline from the Treasury to slash its debt and gain concessions from the UAW or face possible bankruptcy.

Large GM bondholders were aware that the company was planning on missing a big payment, according to a person familiar with the thinking of a committee that holds just under half of the company’s bonds.

This person said the June 1 government restructuring deadline wasn’t a coincidence; the government didn’t want the struggling company to spend $1 billion to keep servicing its debt.

Portfolio manager Greg Hopper of the Artio Global High Income Fund said that at this point, most holders of auto-related debt are professional distressed investors and know what they’re getting into.

Young also said GM has begun pursuing outside investors for its Opel division in Germany. There has been speculation that Fiat SpA, the Italian auto maker vying for a Chrysler LLC alliance, could pursue a stake in Opel and Young said he isn’t ruling out that company.

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