Moody's Investors Service late Monday downgraded Ford Motor Co. F, -2.25% debt rating to Ba1, the first rung of "junk," or non-investment speculative grade, from Baa3. The outlook is stable, Moody's said. The downgrade reflects "considerable operating and market challenges facing Ford, and the weak earnings and cash generation likely as the company pursues a lengthy and costly restructuring plan," the debt ratings agency said. Ford has embarked on a long-term restructuring plan with about $11 billion in charges, and a cash cost of about $7 billion. "Ford is undertaking this restructuring from a weak position as measures of cash flow and profit margins are below our expectations, and below the performance of investment-grade rated auto peers," Moody's said. Cash flow and profit margins are likely to remain weak and Ford faces such difficulties at a time auto markets are softening, it said. Ford "does have a sound balance sheet and liquidity position from which to operate," Moody's said. Shares of Ford fell nearly 2% in the extended session, after ending the regular trading day up 2.1%.