HOUSTON — Public opinion is changing when it comes to legalizing pot, but one of the state's largest police organizations still opposes relaxing marijuana laws. 

Representing more than 30,000 active and retired law enforcement officers, Kevin Lawrence of the Texas Municipal Police Association says, like the public, opinions among police vary when it comes to pot.

"Any effort to decriminalize, legalize, whatever you want to call it – we're not really concerned about that as much as we are: will it increase usage?" said Lawrence.

He says more usage would presumably lead to more impaired driving. Call it DWH if you will: "driving while high."

"Our concern is that it's very difficult right now to determine the level of impairment – especially on the side of the road" said Lawrence.

Currently, Lawrence says there's no scientifically accepted, court-approved, or standardized field sobriety test for marijuana, at least in the U.S. 

And officers known as "drug recognition experts," who are skilled in detecting drug-induced impairment, are few and far between.

Only about 200 are on the job in all of Texas.

"And the officers have to be given the proper training and the proper resources to do whatever enforcement is expected of them" said Lawrence.

Until that happens, the TMPA and others say they can't fully support weakening marijuana laws.

"We enforce the laws that the legislature hands down, pure and simple, whether we agree with them or not." said Lawrence. He also said there is currently too much gray area. 

There are more than two dozen bills in the Texas legislature trying to legalize marijuana in some form.