New York Times Co. raised $250 million from Mexican billionaire Carlos Slim after agreeing to pay an interest rate of more than 14%, the latest in a series of moves by the newspaper publisher to shore up its finances.

The notes Mr. Slim will receive in return for the investment include warrants that can be converted into 15.9 million common shares at a strike price of $6.36, a slight discount to where the shares closed on Friday. The notes, which carry a 14.1% coupon, are due in 2015.

It...