A Rhode Island fabrics company violated the state’s medical marijuana law when it refused to hire a paid intern who had medical permission to use the drug, a state superior court judge ruled.

The case illustrates the need for Rhode Island companies to balance disability rights afforded under the state’s medical marijuana law with their own drug and safety requirements.

The May 23 ruling is problematic for employers, particularly manufacturers, said Mark W. Freel, attorney and board member of the Rhode Island Manufacturers Association. Employees who come to work high can present serious safety problems, he said.

“The judge is...