The National Rifle Association (NRA) is suing Seattle over a city law requiring gun owners to lock up their firearms.

The lawsuit, brought by the NRA along with the Second Amendment Foundation and two city residents, was filed late last week in King County Superior Court in Washington state, which has a regulation prohibiting cities from issuing firearms regulations.

“Seattle simply can’t break the law to adopt an ordinance as a political statement,” Foundation founder Alan Gottlieb said in a statement.

The legislation the lawsuit is opposing was passed earlier in July by a unanimous vote in the City Council.

Proposed by Mayor Jenny Durkan, the law says a gun owner could be fined up to $500 £380) if a firearm is not locked up and up to $1,000 (£761) if a minor, “at-risk person,” or unauthorised user accesses the weapon.

Gun owners can also face a fine of up to $10,000 if someone uses the weapon to injure someone or commit a crime.

Ms Durkan said on Twitter that in addition to the city, the lawsuit names her and recently-chosen Police Chief Carmen Best personally as defendants.

“If they think we are intimidated, they are mistaken,” Ms Durkan said, adding that she “will continue to fight for our kids”.

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Earlier this year she attended the National School Walkout protest on 14 March. Children walked out of schools to call for gun control reform in the wake of several school shootings. Ms Durkan said, holding a copy of the US Constitution: "I believe in the second amendment, but I've read this thing called the Constitution, and second amendment, meet the first amendment" about the right to free speech.

Given the national debate on gun control reform in the wake of several mass shootings - Las Vegas in October 2017 and the spate of school shootings including Parkland, Florida and Santa Fe, Texas - the lawsuit was not unexpected by pro gun-control groups including the nonprofit Everytown for Gun Safety and the law firm Orrick LLP, whose officials said previously they would represent Seattle at no charge.

“Frankly, this is no surprise,” City Attorney Pete Holmes said in a statement.

March for Our Lives – in pictures Show all 13 1 /13 March for Our Lives – in pictures March for Our Lives – in pictures Demonstrators chant during the protest for gun legislation and school safety AP March for Our Lives – in pictures Trevon ‘Tre’ Bosley, 19, of Chicago, the brother of Terrell Bosley who was killed in 2006 in a case of mistaken identity, speaks during the rally AP March for Our Lives – in pictures Marjory Stoneman Douglas High School student Delaney Tarr speaks at the rally AFP/Getty March for Our Lives – in pictures Protestors line the streets in Washington Getty Images March for Our Lives – in pictures People arrive for the March For Our Lives rally against gun violence in Washington, DC AFP/Getty March for Our Lives – in pictures Protestors carrying placards in Washington AFP/Getty March for Our Lives – in pictures Protestors hold up placards in Washington AFP/Getty March for Our Lives – in pictures Schoolchildren wear targets ahead of the rally Getty March for Our Lives – in pictures Attendees congregate in preparation for the march Getty March for Our Lives – in pictures Students brought a host of innovative placards AFP/Getty March for Our Lives – in pictures The movement’s main demand is the banning of assault rifles Getty March for Our Lives – in pictures Since the Florida shooting, students have called for urgent gun reform AFP/Getty March for Our Lives – in pictures In the wake of the Florida attack, President Donald Trump called for teachers to be armed AFP/Getty

“The Mayor and Council are trying to prevent children from accessing guns with this Safe Storage legislation. If the NRA and SAF want to be on record fighting responsible gun ownership, that’s their choice,” Mr Holmes said.

Seattle residents Omar Abdul Alim and Michael Thyng are plaintiffs in the case and cite a fear of home invasions for keeping their firearms unlocked.

This is not the first time the powerful and well-funded gun rights lobbying membership organisation has sued the city, home to headquarters of companies like Microsoft, Starbucks, and Amazon.

In 2010, Seattle introduced a ban on firearms in city parks. The same groups sued the city and the law was ultimately ruled unconstitutional, violating citizens’ right to bear arms.

Last year, however, the Washington state Supreme Court ruled in favour of Seattle’s tax on guns.