WASHINGTON, Dec. 21 (Xinhua) -- Mayor of U.S. capital city Washington, the District of Columbia, has signed a controversial physician-assisted suicide bill, local media reported Tuesday.

The bill, if getting through Congress, will allow terminally ill but mentally capable patients, aged 18 years or older, to legally end their lives.

According to the bill, which the D.C. Council approved in November, doctors will be allowed to prescribe fatal medication to patients with less than six months to live. These patients must make two requests over a period of two weeks and ingest the drugs themselves.

D.C. Mayor Muriel Bowser signed the legislation on Monday, clearing it to be sent to Capitol Hill for a 30-day review, according to Washington Post.

However, it is unclear if Congress will approve the legislation, said the report, noting that local opponents of the law have vowed to press the Republican-controlled Congress to void the bill.

Under the U.S. Constitution, Congress has to sign off on all D.C. laws. If approved, the earliest date the law would take effect would be next October.

"Every terminally ill adult should have the freedom and liberty to make their own decisions about how they want to die in comfort and peace, in consultation with their family, physicians and spiritual leaders," said Donna Smith, an organizer with the national right-to-die advocacy group Compassion and Choices.

Since 1998 when Oregon became the first U.S. state enacting physician-assisted suicide law, the practice has now been considered legal by a court ruling in Montana while by similar laws in the states of Washington, Colorado, Vermont and California.