All of Puerto Rico’s $12 billion of newly restructured sales-tax bonds are tax-exempt, the U.S. Internal Revenue Service has ruled, a boost for the securities in which the tax status of about 30% of the debt was in limbo.

Puerto Rico’s Sales Tax Financing Corp., known as Cofina, the commonwealth agency that sold the bonds, plans to allow investors on or before May 31 to exchange the securities for ones that are tax-exempt, according to a filing posted May 15 on the Municipal Securities Rulemaking Board’s website. The IRS on May 15 notified Cofina that the $3.59 billion of Series...