Mizuho Bank has begun divulging its in-house interest-rate guidelines to corporate borrowers in the hope of persuading them to pay higher interest rates, Mizuho officials said Wednesday.

What the bank terms "interest guidelines" call for higher rates on borrowers whose creditworthiness is ranked at relatively low levels, the officials said.

It assigned 15 ratings to all its corporate borrowers in April, when it was founded along with Mizuho Corporate Bank through the reorganization of member lenders of the Mizuho Financial Group on April 1.