Standard & Poor's (search) Monday cut its ratings on General Motors Corp. (GM) deeper into junk status and said it may cut them again, citing the bankruptcy filing of GM's largest supplier, Delphi Corp. (DPH).

The downgrade could further hamper GM's access to funding, which was already hurt when S&P first downgraded the world's largest automaker to junk status in May.

Delphi's bankruptcy could impede GM's efforts to turn around its ailing North American vehicle operations, S&P said in a statement.

GM will likely face demands from Delphi for price relief and is also exposed to the risk of supply disruptions caused by labor strife at Delphi as the parts supplier downsizes its work force, S&P said.

GM's troubles have worsened in recent weeks after two major hurricanes drove U.S. gasoline prices over $3 a gallon, curbing demand for the automaker's profitable SUVs. GM posted a 24 percent drop in vehicle sales in September with sales of SUVs and trucks off 30 percent.

GM's bonds with an 8.375 percent coupon due in 2033 fell to 76 cents on the dollar from 77.5 cents on Friday, according to MarketAxess.

Ratings of GM's finance arm, General Motors Acceptance Corp. (search) , and its mortgage unit Residential Capital Corp. were not changed but are on review with "developing" implications, meaning they may be upgraded or lowered.

The potential for an upgrade reflects the chance that GM may separate these units from their parent by changing their ownership, S&P said.

"Such an outcome now seems more likely to occur, given the increased challenges that GM is facing," S&P said.

S&P cut GM's long-term rating by one notch to "BB-minus" from "BB." The rating remains on review for another downgrade. GM and its financial unit had $284 billion of consolidated debt at the end of June.