Moody's: Government shutdown could hurt America's top credit rating

The United States' credit rating could come under pressure if the government shuts down, Moody's Investors Service cautioned Monday.

A shutdown would be "credit negative" for the US sovereign, according to a Moody's note.

"While government debt service payments would not be impacted and a short-lived shutdown would be unlikely to disrupt the economy, it would underscore the weakness of US institutional and governance strength relative to other AAA-rated sovereigns that we have highlighted in recent years," Moody's wrote.

"In particular, it would demonstrate the significant constraints that intensifying political polarization put on fiscal policymaking at a time of declining fiscal strength, driven by widening fiscal deficits and deteriorating debt affordability."

The federal government could shut down on October 1 if Congress is unable to pass a federal spending bill.

Moody's is the only one of the three major credit rating agencies to assign the United States an outstanding rating of AAA. Standard and Poor's downgraded the United States in 2011, following the debt ceiling standoff then. In August, Fitch Ratings knocked America's credit rating down to AA+ after the most recent debt ceiling debate.

"Looking ahead, weaker fiscal policymaking that leads to persistently high fiscal deficits and higher than expected interest costs would put pressure on the US rating or outlook," Moody's wrote.