IRS word on the tax treatment of cryptocurrency transactions may come within the next month, after several years of waiting by the digital currency industry and tax professionals.

“We’ll have guidance coming out very soon—could be within the next 30 days, could be even less than that,” Internal Revenue Service Commissioner Charles Rettig said May 30 at a Federal Bar Association conference. “I think it’s going to be helpful” for people who might be guessing at ways that digital assets...