WASHINGTON (Reuters) - U.S. Republican lawmakers on Wednesday stepped up their scrutiny of environmental groups’ work with foreign countries, requesting that the Center for Biological Diversity turn in a list of documents detailing their work with Japanese officials.

It was the third action that Representatives Rob Bishop and Bruce Westerman have taken this month to put a spotlight on foreign governments’ relationship with green groups, who they allege can be used to influence U.S. policy or national security.

Bishop heads the House of Representatives Natural Resources Committee and Westerman chairs the House Subcommittee on Oversight and Investigations.

“The Committee on Natural Resources is continuing its oversight of the potential manipulation of tax-exempt 501(c) organizations by foreign entities to influence U.S. environmental and natural resources policy to the detriment of our national interests,” they said in a letter to the Center for Biological Diversity.

Earlier this month they wrote to the head of the Natural Resources Defense Council, Rhea Suh, asking for details about the group’s work with China on climate change and air quality issues.

Last week, the lawmakers sent a letter to Defense Secretary James Mattis asking him to provide information about environmental litigation against the military by U.S.-based green groups and its negative impact on national security.

Among the examples they cited was a lawsuit led by the Center for Biological Diversity that aimed to block the relocation of a Marine Corps air station in Okinawa, Japan because of its potential harm to a marine mammal, the Okinawa dugong. A court hearing on that case is scheduled for June 28 in a U.S. federal appeals court.

In Wednesday’s letter to CBD President Kieran Suckling, the lawmakers asked for details about that lawsuit, as well as the group’s work with U.S. politicians, press conferences they organized “and other publicity events in support of foreign anti-base activists, environmental groups, and members of the Okinawan government opposed to the U.S. military’s presence.”

“The Committee seeks clarification about the nature of CBD’s advocacy work to influence U.S. environmental and natural resources policy in light of CBD’s close relationship with Okinawan government officials and foreign environmental groups,” the letter said.

A representative for the California-based CBD was not immediately available for comment on whether the group will provide the requested documents. But last week the group said in a statement the lawmakers were pursuing an “anti-wildlife agenda in search of a wild conspiracy theory.”

The lawmakers asked the CBD for a list of documents to be turned in by June 27, including documents that would show whether the group registered as an agent of a foreign principal under the Foreign Agents Registration Act.