Judicial Watch announced on Wednesday it filed suit against the Department of Defense and Army Corps of Engineers, seeking to obtain communications between government officials in the Obama administration and environmental groups related to protests last year opposing the Dakota Access pipeline.

The conservative watchdog group’s Freedom of Information Act lawsuit, filed June 29 in the U.S. District Court for the District of Columbia, charges that the Obama administration and environmentalists worked “hand-in-glove” to try to stop the pipeline’s construction and asks to review communications between the two camps to prove it.