A Montana wildlife advocacy group is suing the U.S. Department of Agriculture in a bid to force officials to turn over documents related to the management of wild bison from Yellowstone National Park.

Attorneys for the Buffalo Field Campaign say the group has received incomplete information or none at all from six public records requests filed since March 2011 under the federal Freedom of Information Act.

The requests were for documents pertaining to programs for bison relocations and population control, tracing reports for diseased cattle in Idaho, Montana and Wyoming and other issues.

Buffalo Field Campaign habitat director Darrell Geist said Tuesday that federal officials appear to be unlawfully denying the requests through a pattern of delay.

The case is assigned to U.S. District Judge Donald Molloy in Missoula.