Those organizations include some of the nation’s preeminent conservative and libertarian nonprofit groups. The AG is requesting Exxon Mobil communications with the Heritage Foundation, the Cato Institute, the Federalist Society, the Hoover Institution, the Reason Foundation, and the Mercatus Institute, among other groups.

One target of the subpoena, the libertarian Competitive Enterprise Institute, has already publicly responded to Walker. Its attorney called the attorney general’s subpoena “a blatant attempt to intimidate and harass an organization for advancing views that you oppose.”

“Your demand on CEI is offensive, it is un-American, it is unlawful, and it will not stand,” wrote Andrew M. Grossman, an attorney with the Washington firm BakerHostetler. “You can either withdraw it or expect to fight.”

Walker’s efforts will likely meet similar resistance from other organizations targeted by the subpoena, some of which have publicly denounced it in reference to its targeting of CEI.