Since fully legalizing marijuana in January, Washington state reported this week a three-fold spike in marijuana-related arrests for suspected impaired driving.

The Washington State Patrol reported some 745 motorists had tested positive for marijuana’s psychoactive ingredient, delta-9-tetrahydrocannabinol (THC). More than half of them yielded test results above the state’s new legal limit for driving, 5 nanograms of THC per milliliter of blood.

Those numbers compare to 1,000 such arrests over a two-year period prior to the legalization of marijuana for recreational use. Yet, some say police are simply using the new law as a pretext to stop more motorists on suspicion of impaired driving, particularly people of color.

Douglas Hiatt, a criminal defense lawyer and marijuana advocate based in Seattle, told Reuters the state’s new marijuana regulations go too far in empowering police to stop motorists for suspected impaired driving. State law, however, forbids police from using sobriety checkpoints.

Although favoring marijuana legalization, Hiatt said he opposed the state’s new law for its stringent driving provision, which holds a zero-tolerance standard for drivers under age 21. That standard makes young adults particularly vulnerable to police looking to fill arrest quotas. "It's like shooting fish in a barrel," he said. "It hits the kids of color the hardest."

Bob Calkins, a spokesman for the Washington State Patrol, said the preliminary findings suggest more people in the state may be driving impaired following marijuana legalization. Calkins specified that although marijuana-related arrests for suspected impaired driving have risen, the number of police stops has not. Every year, the State Patrol arrests approximately 20,000 motorists for suspected impaired driving offense, with other police agencies in the state matching that number.

Whether driving impaired from alcohol, marijuana, or other drugs, Calkins said, "It all comes back to a bad decision to drive while impaired.”

Kevin Sabet, co-founder of Project Smart Approaches to Marijuana, an organization opposing relaxed standards on the drug, told Reuters he found the data troubling. "People are getting the impression that marijuana use is okay," he said. "Even before one recreational store opens in Washington, we are already seeing the effects."

Thus far, retail stores selling marijuana have yet to open in the state as the law continues to take effect. Approved by voters last November, the measure had advanced to a referendum after lawmakers adjourned with no action on the original bill. Along with a similar vote in Colorado, Washington's election represented a world first, and drew 81 percent of the electorate.