(WHTM) — Gov. Josh Shapiro joined several states to send a message to President Donald Trump as his administration deploys National Guard troops across the United States.

The governor filed an amicus brief on Wednesday in a federal appeals court, joining dozens of other states. In it, states argue the president’s out-of-state deployment of troops to Oregon is unlawful and “flouts the vision of our Founders.”

“I filed that amicus brief last night to make very, very clear that the Pennsylvania National Guard, under the leadership of General Pippy, is under my command,” Shapiro said in Philadelphia on Thursday morning. “I’m the Commander in Chief of the Pennsylvania National Guard, and we use the Guard responsibly.”

The brief rests its argument on the principles of federalism, which the states said delegates authority to regulate the National Guard to governors. It also points to historic instances where presidents showed restraint in the domestic deployment of troops.

Trump’s deployment plans have so far targeted Democratic-leaning metropolitan areas, including Los Angeles, Chicago, Portland, and Memphis.

The appeals court is set to decide on the legality of the president’s use of troops in Oregon.

Last month, Shapiro said he’s “prepared” should Trump use troops or federal agents in Pennsylvania cities.

“I think what the president’s doing is wrong. I think what the president’s doing injects chaos in communities,” Shapiro said.

He added, “I’m not going to get into the specifics. I can tell you we are prepared.”

Despite criticism from the Trump administration, Pennsylvania has so far avoided the ire of the president.