Kansas has joined Oklahoma in a lawsuit challenging the process used by the federal government to list the lesser prairie chicken as a threatened species.

Kansas Attorney General Derek Schmidt’s office announced Wednesday that Kansas on Tuesday became part of a case filed earlier this month in federal court in Oklahoma.

Oklahoma filed the lawsuit before the U.S. Fish and Wildlife Service formally listed the lesser prairie chicken as threatened. It argues the service is not following the process spelled out by federal law.

Kansas officials contend that the listing isn’t necessary because the five states with lesser prairie chicken habitats have developed a conservation plan. They are Kansas, Oklahoma, Colorado, New Mexico and Texas.

The federal agency says the lesser prairie chicken’s population has decline dramatically since 2012.