The Climate Science Legal Defense Fund (CSLDF) filed a formal complaint with the U.S. Internal Revenue Service (IRS) against the Mercer Family Foundation on June 27, 2017. The complaint alleged that the Mercer Family Foundation, a tax-exempt 501(c)(3) private foundation, violated its charitable status by funding organizations that engaged in political lobbying and the harassment of climate scientists. The CSLDF contended that these activities, which included supporting groups like the Heartland Institute and the CO2 Coalition known for climate change denial, were inconsistent with the foundation's tax-exempt purpose. The complaint sought an IRS investigation into the foundation's operations and funding practices. The CSLDF reported in 2018 that they had not received any updates from the IRS regarding the complaint. The lawsuit, as it is sometimes referred to, involved the CSLDF's concerns about the Mercer Family Foundation funding organizations that allegedly harassed climate scientists.