WASHINGTON (AP) — Doctors in the nation's capital may now begin the process of prescribing life-ending drugs to terminally ill patients.

The Washington Post reports that rules and regulations to implement the law took effect Monday. The District of Columbia joins Colorado, Oregon, California, Montana, Vermont and Washington in allowing the practice.

Patients older than 18 with less than six months to live are eligible. Two witnesses must attest that a patient is making the decision voluntarily.

The move sets up a showdown with Republicans in Congress trying to void the law. Last week, a U.S. House panel voted to advance a measure that would repeal the Death With Dignity Act. It must be approved by the full House and Senate and the president before it can take effect.