The state regulators overseeing Oregon's recreational cannabis have abruptly curbed the ability of medical marijuana cardholders to buy weed in bulk, citing suspiciously large purchases that were likely leaking into the black market.

The Oregon Liquor Control Commission on Aug. 23 approved an emergency temporary rule that limits the amount of marijuana medical cardholders can buy each day to one ounce.

That's the same amount of cannabis that anybody else over 21 can buy in Oregon. But cardholders had been granted a special dispensation, allowing them to buy up 24 ounces per day.

That allowance was an effort by state officials to help people who used cannabis as medicine to make tinctures. Advocates also wanted to make sure people who lived in the "dry" counties east of the Cascades—areas where local weed bans are so prevalent that they are called "cannabis deserts"—could buy their medicine without constant travel.

But this week, OLCC officials looked at data on sales to medical cardholders—and found trends suggesting some people were buying weed to sell in dry counties or in other states.

"There were some significant numbers of people doing that—including people who were going in every day and buying the maximum," says OLCC spokesman Mark Pettinger. "There was at least one individual who was purchasing six to eight pounds a week. That's a lot of flower for people to consume or gift in a week. It raises some suspicions."

Stopping the leakage of legal weed into the black market is a top priority for the OLCC. Oregon has harvested too much cannabis—making prices drop to record lows and tempting desperate growers to sell into the black market. That's a dangerous game when federal officials, led by U.S. Attorney General Jeff Sessions, have pledged to crack down on legal-weed states that leak pot across state lines.

So the OLCC voted this week to cap sales to medical cardholders until Dec. 27.

"Given the fact that we are under scrutiny, we needed to step in and take some quick action," Pettinger says. "We're going to take a deeper dive."

The Oregon Cannabis Association, a weed industry trade group, pledged to work with the OLCC to fix any potential problem and let medical cardholders buy in bulk again.

"The OCA continues to support patients' access to medicine," it said in a statement. "We are actively engaged with the OLCC to ensure that there is emergency rule-making path forward to combat the illicit market and diversion, while ensuring patients everywhere have access to the amounts of medicine that they need."