Long-term credit rating of General Motors Corp. has been lowered by Moody’s Investors Service, one of the three biggest rating companies, to Baa3, closing the world’s largest auto maker to speculative grade. It also cut by one notch the long-term rating of the company’s finance branch, General Motors Acceptance Corp., to Baa2. The forecasts for the future of both companies ratings seem negative.

As a result of the Moody’s downgrade, GM’s bond rating entered nearly the same level by those of Standard & Poor’s and Fitch Ratings.

Moody’s said the downgrade of GM’s ratings is caused by the tendency that the auto maker faces "formidable long-term challenges in the company’s automotive operations." The same reason is to explain the GMAC’s downgrade.

Moody’s is the only major rating firm that rates the auto makers and their finance units differently.

Acting as the only major rating firm that deals with the auto manufacturers, Moody’s also took the long-term ratings of Ford Motor Co. and Ford Motor Credit into consideration as to possible downgrade.