PROVIDENCE, R.I. – The federal government is warning Rhode Island against licensing Canadian pharmacies to sell prescription drugs.

The Rhode Island law allows for the state Board of Pharmacy to license Canadian pharmacies in the same way it licenses other mail-order pharmacies located out of state. The law went into effect on Jan. 19, when Gov. Don Carcieri let the bill become law without his signature.

No Canadian pharmacy has applied since the law went into effect.

The warning came in a letter the Food and Drug Administration sent to state Attorney General Patrick Lynch on Friday. It provides legal reasons for opposing the law but does not explicitly urge Lynch to act, nor does it say what the FDA would do if Rhode Island moved ahead.

“We weren’t intending to make any threats,” William Hubbard, the FDA’s associate commissioner for policy and planning and the letter’s author, told The Providence Journal.

“We’re trying to help people understand there are significant federal legal issues here. When the pharmacy board gets the first license application, we wanted to make sure they understand that they would be licensing pharmacies that are importing illegal drugs.”

Lynch’s spokesman, Michael Healey, said that the attorney general was reviewing the letter, and had no immediate comment.

A spokesman for the state health department had no comment other than saying the letter is a legal issue, rather than a health one.

Many residents favor buying their medications from Canadian suppliers, where they are often significantly cheaper because of government price controls. Opponents argue the drugs could be dangerous, because there’s no proof where they’re manufactured.

Several city mayors and Secretary of State Matt Brown favor importing Canadian drugs.

Even before the Rhode Island law was passed, scores of residents made bus trips across the border to buy their medicines in Canada.

Congress has considered legalizing the importation of prescription drugs but has met strong opposition from the White House and the pharmaceutical industry.