Shares in Countrywide Financial Corp. closed down more than 12 percent Monday in anticipation that the nation’s largest mortgage lender’s credit rating would be downgraded to junk status by Moody’s Investors Service.

The ratings service, however, affirmed Countrywide’s rating at Baa3, sending shares up 2.1 percent in after-market trading.

Craig Emrick, a spokesman for Moody’s, said in the report that the outlook for all ratings for the Calabasas-based lender is negative. He added that Moody’s “considers it likely the company will experience additional markdowns and elevated provisioning in the coming quarters, possibly resulting in additional consolidated losses, but not to the extent of significantly impairing capital.”

Traditionally, when a company’s debt rating is downgraded from “investment” grade to “junk” status, it forces large pension funds and institutional investors to sell the debt because they are prohibited from holding such bonds. In addition, it costs companies more to borrow money as investors demand higher yields due to the greater perceived risk of the debt.

Shares in Countrywide closed down $1.50, or 12 percent, to $10.57 in trading Monday on the New York Stock Exchange but got back a little of the loss, gaining 3.5 percent in after-market trading to $10.94.