U.S. President Barack Obama offered some encouraging words for advocates of marijuana reform: Look for change at the federal level. As more states legalize or decriminalize pot, it could pressure Congress to reconsider classifying it as a Schedule I drug, a category it shares with heroin and LSD, the president said during an interview with VICE News on Monday.

“We may be able to make some progress on the decriminalization side,” the president said. “At a certain point, if enough states end up decriminalizing, then Congress may then reschedule marijuana.”

Fifteen states in the U.S. have decriminalized marijuana, including 10 that have also legalized medical marijuana. An additional eight states allow medical marijuana but have not decriminalized the drug for non-medical patients; four states and the District of Columbia have fully legalized cannabis. Hundreds of local municipalities across the country have adopted their own ordinances decriminalizing pot possession. Despite those laws, the drug remains illegal at the federal level.

As of March 9, there were 13 states with pending legislation to legalize medical marijuana in 2015. Bills meant to allow patients access to medical pot were defeated in Mississippi and North Dakota earlier this year.

President Obama went on to distinguish between decriminalization, which typically means first-time offenders caught with small amounts of marijuana won’t get prison time or a criminal record, and encouraging its use. “Our criminal justice system is so heavily skewed toward cracking down on non-violent drug offenders that it has not just had a terrible effect on many communities…it costs a huge amount of money to the states and a lot of states are starting to figure that out,” Obama said. He said such laws particularly affect communities of color, which makes it hard for them to get work because of a felony record. “Legalization is not a panacea, [but] locking somebody up for 20 years is probably not the best strategy,” the president said.

Supporters of federal marijuana reform applauded the president’s comments, but said that the issue is more important than Obama let on. “The president is right that as voters force more and more changes to state marijuana laws, national policymakers will have no choice but to catch up,” Tom Angell of MarijuanaMajority.com said in an emailed statement. “On average, there's a marijuana possession arrest in the U.S. about every minute. Billions of dollars are wasted on enforcing prohibition laws that don’t stop anyone from using marijuana but do ruin people’s lives with damaging criminal records.”

He added that “this is a serious issue, and the president needs to treat it as such.”