Lawmakers are reluctant to reopen legislation on the sales tax rise, raising the bar for Prime Minister Shinzo Abe should he seek a shallower path of increases, according to one of his advisers.

"They don't want to touch on this issue," Etsuro Honda, 58, a Shizuoka University professor and one of the brain trust members behind Abe's reflation plan, said Wednesday in Tokyo, referring to a majority of lawmakers.

"I'm fully aware that I'm in a minority" that favors a flatter trajectory for boosting the levy than the current law provides, he acknowledged.