The Nature Conservancy’s review calls into question millions of dollars of credits sold to JPMorgan, BlackRock, and Disney.

Following concerns that it is facilitating the sale of meaningless carbon credits to corporate clients, the Nature Conservancy says it’s conducting an internal review of its portfolio of carbon-offset projects. The nonprofit owns or has helped develop more than 20 such projects on forested lands mostly in the U.S., which generate credits that are purchased by such companies as JPMorgan Chase & Co., BlackRock Inc., and Walt Disney Co., which use them to claim large reductions in their own publicly reported emissions.

The self-examination follows a Bloomberg Green investigation last year that found the world’s largest environmental group taking credit for preserving trees in no danger of destruction. The internal review is a sign that it’s at least questioning some practices that have become widespread in the environmental world, and could carry implications for the broader market for carbon credits.

While the Nature Conservancy declined to answer specific questions about the review, it said in a statement that it aims to meet the highest standards with its carbon projects and that the inquiry will be led by scientists and a “team of experts with deep project knowledge.”