The industry is "using a shotgun to kill a couple of flies," said John Ulzheimer, president of educational services for Credit.com in San Francisco, which provides credit and personal finance services. Ulzheimer, who used to work for Equifax and Fair Isaac, said consumers without established credit scores will have a difficult time obtaining loans or applying for credit online or through an automated system - and they probably won't realize why. The majority of those affected by the formula change are women, he added.

"When people get married, one of the spouses changes the way they use credit, and in more cases than not it's the woman," Ulzheimer said. "The problem is that 50 percent of people in this country who get married also get divorced. If these people have nothing but authorized-user history, they'll be starting with a new credit score."

Gail Cunningham, spokeswoman for the National Foundation for Credit Counseling, a financial counseling and services organization, said those whose credit scores are built on authorized-user account histories should try to establish their own line of credit before the formula change takes effect.