The attorneys general for Nebraska and Oklahoma filed a lawsuit Thursday, asking the U.S. Supreme Court to overturn Colorado's voter-approved law that legalized the sale of marijuana this year.

Nebraska Attorney General Jon Bruning told reporters Thursday that federal law "undisputedly prohibits the production and sale of marijuana," and that by legalizing it, Colorado "has undermined the United States Constitution."

Authorities have complained that marijuana sold legally in Colorado has been crossing state lines where it is illegal and, they say, having an adverse effect on their communities.

Colorado Attorney General John Suthers said the lawsuit wasn't a surprise but vowed to vigorously fight it should the Supreme Court decide to hear the case.

"Because neighboring states have expressed concern about Colorado-grown marijuana coming into their states, we are not entirely surprised by this action," Suthers said in a statement. "However, it appears the plaintiffs' primary grievance stems from non-enforcement of federal laws regarding marijuana, as opposed to choices made by the voters of Colorado. We believe this suit is without merit and we will vigorously defend against it in the U.S. Supreme Court."