Colorado faces new opposition to its legalization of marijuana sales for recreational use, as a third lawsuit seeking to roll back the measure was filed Thursday. A number of county attorneys and sheriffs in Colorado, Kansas and Nebraska joined the suit against Colorado Gov. John Hickenlooper to reinstitute marijuana prohibition and shutter the more than 330 licensed marijuana stores around the Rocky Mountain State.

Filed with the U.S. District Court in Denver, the lawsuit’s primary argument is that Amendment 64, the ballot measure approved by Colorado voters in 2012 that legalized marijuana for adults older than 21 years of age, “is preempted by federal law and therefore violates the Supremacy Clause (Article VI) of the United States Constitution.”

Lead plaintiff Justin E. Smith, sheriff of Larimer County in Colorado, called the case a “constitutional showdown,” according to to USA Today. He argued that he must decide every day whether to violate the Colorado Constitution or the U.S. Constitution.

“Amendment 64 pursues only one goal -- legalization of marijuana -- a goal which is diametrically opposed to the many objectives which Congress has established, and repeatedly reestablished, for the United States’ anti-drug policy and practice for marijuana as a controlled substance,” the lawsuit states. “If allowed to continue in effect, Amendment 64’s legalization and commercialization scheme will conflict with and undermine the federal government’s careful balance of anti-drug enforcement priorities and objectives.” The suit seeks declaratory and injunctive relief.

Advocates of keeping Colorado’s marijuana-legalization measure on the books dismissed the lawsuit, saying those working to repeal Amendment 64 are “on the wrong side of history.”

“While a growing majority of Americans supports replacing failed prohibition policies with legalization, there will always be some people who desperately try to cling to what’s familiar,” Marijuana Majority Chairman Tom Angell said via email. “The people of Colorado and other states have spoken, and now these prohibitionists who lost at the ballot box on Election Day are trying to overturn the will of the voters by making a last-ditch attempt in the courts. They are wrong about marijuana policy, and they are on the wrong side of history.”

The latest lawsuit is the third legal action this year aimed at overturning Colorado’s legalization of marijuana. Both filed at the behest of the anti-drug organization Safe Streets Alliance, the two previous suits allege that by allowing for a regulated marijuana market, state lawmakers are breaking federal law, which considers the plant illegal.

Colorado was also sued by the Nebraska and Oklahoma attorneys general over its legalization of marijuana. Colorado has not yet responded to that lawsuit, and the state has until March 27 to defend its policy before the U.S. Supreme Court, the Associated Press reported.

Hickenlooper has not been served with papers in the latest lawsuit, USA Today reported, but Colorado Attorney General Cynthia Coffman is expected to contest it on the state's behalf. “The Colorado Attorney General will defend the Colorado law from this challenge,” Coffman’s spokeswoman Carolyn Tyler said, according to Denver Post's The Cannabist. She said she could not comment further because Coffman has not yet been served.

Hickenlooper has said in the past that he respects the will of Colorado’s voters in defending the law and has sought guidance from the federal government.

The U.S. Justice Department announced in 2014 it would take a hands-off approach in states that have legalized marijuana as long as regulations are designed to keep marijuana away from children and out of the hands of criminals.

Marijuana Policy Project representative Mason Tvert said he is unaware of any other marijuana-related lawsuits targeting Colorado, and hopes no others are coming. “They are really just wasting our tax dollars to defend them,” Tvert said. “I can’t say if others will come out, but I think we’re in a situation that is overall kind of similar to marriage equality where we see states moving forward and you see the federal government moving in a direction of acceptance, and there are still some individuals who are resisting that shift in culture and law.”

Read a copy of the latest lawsuit below.

Sheriffs Sue Colorado Over Legal Marijuana by tomangell