Federal drug-enforcement agents earlier this week seized medical-marijuana samples from a Denver lab that does potency testing for dispensaries, in what cannabis advocates say is an instance of continued official harassment of the medical-marijuana industry.

The raid at Full Spectrum Laboratories, just north of downtown Denver, occurred Wednesday, said Betty Aldworth, the lab’s outreach director. She said agents took dozens of medical-marijuana samples — either small pieces of plants or test tubes of “extraction fluid” — but left the lab’s equipment and did not arrest anyone.

Neither a Drug Enforcement Administration spokesman nor a U.S. attorney’s office spokesman would confirm or deny that the raid took place. Documents that would reveal why federal authorities targeted the lab were not available Thursday.

“We cannot comment on ongoing federal investigations,” DEA spokesman Mike Turner said.

Rob Corry, an attorney for the lab, also declined to comment.

Aldworth said lab employees are baffled as to why DEA agents would raid the lab. She said the lab is designated as a caregiver for several medical-marijuana patients in the state.

U.S. Attorney General Eric Holder announced last year that federal authorities would not bother people operating in compliance with their state’s medical-marijuana laws, but would continue to pursue anyone authorities believed were using the laws as cover for more nefarious activities.

“The advice that we received suggested we were doing everything we needed and more to be legal,” Aldworth said.

The lab, which opened in November, conducts tests on different marijuana strains to determine their potency and help dispensaries provide dosing guidelines for patients.

“It seemed, based on their questioning, they thought we were doing other things here,” Aldworth said.

Meanwhile on Thursday, lawyers for the city of Centennial and a dispensary the city ordered shuttered prepared for round two of their legal fight in an Arapahoe County courtroom.

In December, Judge Christopher Cross ruled that Centennial improperly cited federal law in shutting down the dispensary, CannaMart.

Since the ruling, though, Centennial has prevented CannaMart from reopening, arguing that its current location isn’t zoned for a dispensary and that the city’s moratorium on new dispensaries prevents it from moving elsewhere.

Centennial attorney Andrew Nathan said the city was acting in good faith. But CannaMart attorney Bob Hoban argued that those conditions effectively continued the ban, and he asked Cross to intervene. Cross declined, saying the zoning and moratorium issues weren’t brought up in CannaMart’s original lawsuit.

“If they choose a different reason for banning it . . . that’s a different issue, and that’s not before the court,” Cross said.

CannaMart’s attorneys then vowed to amend their lawsuit to include the new issues, setting up another clash in the ongoing battle.

John Ingold: 303-954-1068 or jingold@denverpost.com