A Republican senator is questioning the Obama administration’s refusal to challenge state laws in Colorado and Washington State that make it legal to smoke marijuana for fun. (21 states and the District of Columbia have legalized marijuana for medicinal purposes.)

“These policies do not seem to be compatible with the responsibility of our Justice Department to faithfully discharge their duties, and they may be a violation of our treaty obligations,” Sen. Chuck Grassley (R-Iowa) told a Justice Department official at a Judiciary Committee hearing on Tuesday.