Upping the pressure on Mitt Romney, a one-time key financial backer is saying the Republican presidential nominee should release his tax returns. 

“Mr. Romney ought to square with the American people and release his taxes like any other candidate,” Jon Huntsman Sr. told The Washington Post Friday afternoon. “I’ve supported Mitt all along. I wish him well. But I do think he should release his income taxes."

The comments could make it more difficult for Romney to stick to his pledge not to release any more tax returns beyond the two years he has already provided. Huntsman Sr., the founder of Huntsman Corporation, served as the national finance chair of Romney's failed 2007-08 bid for the presidency, and has helped raise a significant amount of money for Romney. This time around, he backed his son, former Utah governor Jon Huntsman Jr. 

Speculation has been rife lately that Huntsman Sr., whose business partner was a longtime managing director of Bain Capital, might be the source for Senate Majority Leader Harry Reid's claim that in several years Romney didn't paid any taxes. But Huntsman Sr. denied to the Post that he had ever spoken to Reid about the subject.