BOSTON (AP) – Federal regulators told Mayor Thomas Menino they are “troubled” by Boston’s decision to join the list of cities allowing city workers and retirees to buy prescription drugs from Canada.

The Food and Drug Administration, reiterating concerns it raised late last year, sent Menino a letter Wednesday reiterating concerns that the program could put citizens at risk from drugs of unknown origin and quantity.

The letter, from William K. Hubbard, the agency’s associate commissioner for policy and planning, said, “We are troubled that you would actively promote such unproven and unregulated drugs to your employees and retirees.”

A phone message seeking comment from Menino spokesman Seth Gitell was not immediately returned.

On July 21, Menino went ahead with the plan despite a federal prohibition on the practice.

The FDA says such plans are risky because imported drugs bypass U.S. regulatory controls designed to ensure drug safety and quality.

Menino expects the plan will save about $1 million in its first year by giving city workers and retirees access to medications from Canada, where they are cheaper because of government price controls.

Menino has said the city’s contract with Calgary, Alberta-based Total Care Pharmacy Ltd. includes stringent quality standards and procedural safeguards.

But the FDA’s letter Wednesday said Total Care has failed to abide by an agreement with Wisconsin.

Total Care agreed not to send Wisconsin residents drugs for which there is no U.S.-approved equivalent generic version, but has failed to comply, Hubbard wrote.

“It is selling drugs that are considered risky in a variety of ways, and that it agreed not to export to America,” the letter said.

About 14,000 city workers, retirees and dependents enrolled in the Blue Cross Blue Shield health plan are eligible for Boston’s voluntary Meds By Mail pilot program.

Springfield last year became the first city in the state, and one of the first in the nation, to buy its prescription drugs from Canada. The city saved about $3 million in its first year. Springfield officials expect to double savings in its second year.

Pittsfield and Somerville are also buying prescription drugs from Canadian pharmacies.