Image copyright Reuters

Voters in Washington DC will join those in Oregon and Alaska to decide whether to legalise cannabis on Election Day, the city's election board has said.

The US capital city certified on Wednesday that legalisation supporters had gathered enough signatures to put the measure on the November ballot.

It would allow adults over age 21 to possess up to 2oz (56g) of marijuana and to grow up to six plants at home.

Voters in Colorado and Washington state voted to legalise the drug in 2012.

Civil rights issue

Marijuana remains illegal under federal law, but the justice department has said it will not challenge state laws in states where it is either legal for medical purposes or recreational use.

Washington's city council decriminalised marijuana in May, opting to punish possession of small amounts with a $25 (£15) ticket instead of a hefty fine, jail time and a criminal record. The council is also considering a separate bill allowing the sale and regulation of the drug.

Image copyright Getty Images Image caption Marijuana remains an illegal drug under federal law but US officials are not challenging state laws

Cannabis supporters in Washington DC (DC stands for District of Columbia) have argued legalisation is a civil rights issue. Surveys show blacks and white use marijuana at roughly the same rate, but black Washingtonians are far more likely to be arrested or fined for possession of marijuana.

"The District has one of the country's highest rates of racial disparities in arrest and is right at Congress' doorstep," said retired Maryland State Police Maj Neill Franklin, executive director of Law Enforcement Against Prohibition.

"More and more political leaders from both sides of the aisle are beginning to follow their constituents in recognising that drug policy reform is one of the most effective ways to address the problems of our current criminal justice system."

Self-rule

A survey by the Washington Post suggests 63% of city residents support legalisation, but there is opposition in Congress.

Washington DC is not a state, and under the terms of the city's charter its laws are subject to review by Congress.

A spending bill currently pending in the Senate includes an amendment barring the city from spending money to legalise or reduce penalties for marijuana possession, which would complicate the District's recent decriminalisation move though not overturn it.

A similar legalisation ballot measure was halted 16 years ago by Congress, the Post reports.

But Congress declined to block Washington's decriminalisation ordinance earlier this year, and President Barack Obama has said he will not sign laws interfering with Washington's self-rule.