(Reuters) - Citigroup Inc C.N added restrictions on firearms sales for new retail-sector clients, the Wall Street bank said on Thursday, the strongest move to date by a major U.S. lender following last month's high school shooting in Florida.

The Citigroup Inc (Citi) logo is seen at the SIBOS banking and financial conference in Toronto, Ontario, Canada October 19, 2017. Picture taken October 19, 2017. REUTERS/Chris Helgren

In an emailed statement Citi said it will require those clients only sell firearms to customers who have passed a background check, restrict firearms sales for buyers under 21, and not sell so-called “bump stocks” or high-capacity magazines.

The new rules could be seen as somewhat symbolic since they are unlikely to directly affect a large share of business at the bank, which had total assets of $1.8 trillion at Dec. 31. They come weeks after a shooting at a Florida high school that killed 17 people, the second-deadliest shooting at a public school in U.S. history.

Major retailers and at least one online lender have taken similar steps since the shooting brought new calls for gun safety measures and tighter restrictions.

So far other major banks and financial services firms have focused more on their communications or talks with the weapons industry, including outreach by Bank of America BAC.N and asset manager BlackRock Inc.BLK.N

Avery Gardiner, co-president of the Brady Campaign to Prevent Gun Violence, a Washington, D.C. group seeking weapons restrictions, said Citi’s steps demonstrate changes other financial firms could make.

She praised Citi’s stance on requiring completion of background checks, since current law allows dealers to sell weapons if a background check does not come back in three days. Citi’s move, she said, “is a next big step.”

Lawrence G. Keane, general counsel for the National Shooting Sports Foundation, a trade association for the firearms industry, said in a statement, “These policies do nothing to add to public safety and, in fact, may put vulnerable Americans at greater risk to be victims of crime.” He called Citi’s action “virtue signaling.”

Citi said that in addition to the policy for new clients, it is starting talks with current clients on their practices and if they do not adopt changes the bank will help “transition their business away from Citi.”

In the e-mailed statement, Citigroup CEO Michael Corbat said its new policy “was designed to respect the rights of responsible gun owners while helping to keep firearms out of the wrong hands.”

Corbat, who called himself “an avid outdoorsman and responsible gun owner,” said Citi also will start talks with other finance companies on possible additional steps to improve gun safety. It will also speak with clients that make guns, though the bank has few such relationships, he said.

By most measures the weapons industry represents a small slice of Citi's overall business. It was not among bank groups that arranged loans or bonds for gunmakers Vista Outdoor, Remington or American Outdoor Brands AOBC.O in recent years, according to a review by Thomson Reuters' IFR unit.

Citi was however the lead bank on a recent $550 million bond issue by Olin Corp OLN.N, and since 2012 has participated in three other debt sales for the chemical company that owns ammunition maker Winchester, according to IFR data.

Ed Skyler, executive vice president for global public affairs, said in an interview that Citigroup realizes its tighter rules on guns could cost some business from customers who disagree.

“Our eyes are wide open about what some of the impacts could be,” he said.

Some gun-control advocates have suggested banks and companies involved in payments could restrict sales at certain specialized gun dealers tagged as “bad apples” for loose compliance with gun laws.

Citigroup declined to comment on the idea though it noted in a blog that current payment systems do not allow it to see exactly what items customers are buying at the checkout aisle.

Citi provides store-branded credit cards to various retailers. None currently sell guns but if Citi were in talks with such a retailer, Skyler said, “we would want to see these best practices used at their point-of-sale.”