The Environmental Protection Agency barred The Associated Press, CNN and the environmental-focused news organization E&E from a national summit on harmful water contaminants.
The EPA blocked the news organizations from attending Tuesday's Washington meeting, convened by EPA chief Scott Pruitt.
EPA spokesman Jahan Wilcox told the barred organizations they were not invited and there was no space for them, but gave no indication of why they specifically were barred.
Pruitt told about 200 people at the meeting that dealing with the contaminants is a "national priority."
Guards barred an AP reporter from passing through a security checkpoint inside the building. When the reporter asked to speak to an EPA public-affairs representative, the security guards grabbed the reporter by the shoulders and shoved her forcibly out of the EPA building.