DENVER (CN) — A Denver attorney representing the Colorado River Ecosystem in a bid for “personhood” is facing possible sanctions for refusing to drop the case.

Jason Flores-Williams, a criminal defense attorney, gained national attention in 2016 for a class-action lawsuit against Denver challenging its sweeps of homeless camps.

In September this year, Flores-Williams sued Colorado on behalf of the environmental group Deep Green Resistance, asking that the Colorado River ecosystem be granted personhood in the same way a ship, an ecclesiastic corporation or a commercial corporation have it for purposes of constitutional protection and enforcement.

An assistant attorney general warned Flores-Williams in a Nov. 16 letter that if he did not voluntarily request dismissal with prejudice, he could face sanctions under Rule 11 of the Federal Rules of Civil Procedure, for knowingly presenting false or unwarranted claims to the court.

The letter from Colorado’s Senior Assistant Attorney General Scott Steinbrecher said that Flores-Williams’s amended complaint “fails to disclose law contrary to your position that Eleventh Amendment immunity does not apply,” and that it “fails to address the numerous other deficiencies identified in the State’s Motion to Dismiss.”

It adds: “If you choose not to voluntarily withdraw your Amended Complaint with prejudice by close of business November 30, 2017, you are hereby on notice that the defendant will pursue all sanctions and remedies available under Fed R. Civ. P. 11.”

On Tuesday, Flores-Williams released an open letter to the Attorney General’s Office, stating: “The Amended Complaint will not be withdrawn. Legally, it should not be. Morally, it cannot be.” (A footnote, omitted in the quote above, rebuts Steinbrecher’s 11th Amendment argument.)

Flores-Williams’ 4-page letter chides Steinbrecher for his threat of sanctions.

“The Attorney General’s mandate is to protect and serve the rights of the people of this State, of which the undersigned is an engaged citizen, not to use those vested powers to intimidate and forcibly chill those with whom it does not agree,” Flores-Williams wrote.

In a statement accompanying the open letter, Flores-Williams said: “They didn’t threaten to sanction Exxon attorneys for lying about global warming, nor Bank of America attorneys for fraudulently foreclosing on people’s homes, nor Nestle attorneys for privatizing our water and selling it back to us — but attempt to equal the playing field between corporations and the environment and they try to personally damage you. It’s the playbook.”

The next step, apparently, lies with the Attorney General’s Office.