Veterans Affairs Canada says it's notifying the Office of the Privacy Commissioner after veterans were recently sent a letter in an envelope that outed them as medical marijuana users.

The letter from Veterans Affairs arrived in a Medavie Blue Cross envelope with a window that made the bolded words "Re: Cannabis for Medical Purposes" visible on the envelope for anyone to see.

Veterans and their families expressed concern about the letters, saying it breached their privacy.

Veterans Affairs said it had reviewed the case of the letters from Medavie Blue Cross.

"The review has determined that a material breach of privacy has occurred," Sarah McMaster, a press secretary for the Veterans Affairs minister, said in an email to CBC.

McMaster said the department is taking "corrective action" with Medavie Blue Cross so that letters sent to veterans in the future "respect and protect their privacy."

There are about 3,000 veterans across Canada who use medical marijuana.