This warning comes as the leading credit rating agency emphasizes the importance of Congress continuing to fund the federal government past the end of the current fiscal year on Sept. 30.

Failure to continue funding the government could have dire consequences for the economy and stock markets. According to the rating agency, that would result in a damaging downgrade from the current top "AAA" credit rating enjoyed by the United States.

A Warning From the Credit Rating Agencies

Moody's currently assigns the U.S. government its highest credit rating and gives the country a "stable outlook." However, Moody's is the last major credit rating agency to maintain the highest rating on the United States. Earlier this year, Fitch Ratings downgraded the U.S. government one notch to "AA+." That's the same rating that S&P Global assigned the U.S. back in 2011 following a "similar debt ceiling fight."