Vermont Sen. Bernie Sanders introduced a bill Wednesday that would end the federal prohibition on marijuana, an issue that has boosted his bid for the Democratic presidential nomination.

Sanders's bill calls for marijuana to be removed from the Drug Enforcement Administration's schedule of controlled substances. Marijuana is currently classified by the federal government as a Schedule I controlled substance, the same category as heroin and LSD.

According to pro-legalization groups, Sanders' bill is the first ending federal marijuana prohibition to be introduced in the Senate. Sanders is the only presidential candidate so far this cycle to call for marijuana to be removed from the DEA's controlled substances schedule.

Hillary Clinton, the Democratic front-runner, has said she wants to see how legalization plays out in states like Colorado and Washington before pushing any changes at the federal level. Former Maryland Gov. and Baltimore Mayor Martin O'Malley said he supports putting marijuana on Schedule 2, a category that includes drugs like cocaine, opium and morphine.

Last week at a town hall at George Mason University in Virginia, Sanders told college students that "in my view, the time is long overdue for us to remove the federal prohibition on marijuana."

"In my view, states should have the right to regulate marijuana the same way that state and local laws now govern sales of alcohol and tobacco," Sanders said at the town hall, which was livestreamed to roughly 300 college campuses across the country.

Thus far, four states — Colorado, Washington Oregon and Alaska — have legalized recreational marijuana. On Tuesday, Ohio voters Ohio voters rejected a ballot proposal that would have legalized both recreational and medical marijuana — but would also have given one group of investors monopoly power over the state's pot business.

Sanders's bill would not instantly make marijuana legal across the country. That decision would be left to individual states.