The Bank of Japan should ditch its negative interest rate policy because it is spreading unease among savers and small companies, the main opposition party said a month ahead of an Upper House election.

Shiori Yamao, 41, a former public prosecutor turned policy chief of the Democratic Party, spoke in an interview on Tuesday at her offices in Tokyo. Days earlier, the ruling Liberal Democratic Party issued an election platform that had no reference to monetary policy, whereas monetary easing by the Bank of Japan had been a centerpiece of past election agendas.

"The Democratic Party wants to call for the withdrawal of negative interest rates," Yamao said. "Negative interest rates shift the burden onto savers. They cause unease among smaller companies because they make financial institutions unwilling to loan, or prompt them to call loans in early," she added. Her party will call for a more flexible monetary policy, she said.