The Environmental Protection Agency repeatedly broke the law and engaged in "covert propaganda" when it conducted social media campaigns to trump up support for a controversial regulation that gives the agency authority over small streams of water, congressional auditors said Monday.

The Government Accountability Office (GAO) said in a new report that the EPA's social media campaigns promoting its Waters of the United States rule violated laws that bar federal agencies from lobbying or promoting its own actions, according to the Hill.

Auditors took specific issue with the EPA's use of the social media amplification tool Thunderclap, which the agency used to encourage hundreds of Twitter users to redistribute favorable messages about the rule without disclosing the EPA as the source of the messages. The social media campaign also asked users to submit comments on the draft water rule, and reached at least 1.8 million people, according to Fox News.

"We conclude that EPA's use of Thunderclap constituted covert propaganda, in violation of the publicity or propaganda prohibition," wrote GAO in its 26-page report.

"We also conclude that EPA hyperlinks to the [Natural Resources Defense Council] and Surfrider Foundation webpages provided in the EPA blog post constitute grassroots lobbying, in violation of the grassroots lobbying prohibition."

The Obama administration said the rule, also known as the Clean Water Rule, is intended to clarify which streams and wetlands are protected under the Clean Water Act, and would safeguard drinking water for 117 million Americans. However, opponents say the regulation vastly expands the EPA's authority and could result in federal regulation of every stream and ditch.

More than half the states have filed legal challenges, and federal courts have put the regulations on hold until the lawsuits can be considered.

The EPA said it disagrees with the GAO's assessment and defended its social media practices.

"We maintain that using social media to educate the public about our work is an integral part of our mission," said the agency's statement, according to Politico. "We have an obligation to inform all stakeholders about environmental issues and encourage participation in the rulemaking process. We use social media tools just like all organizations to stay connected and inform people across the country about our activities."