The White House has refused to release a photo of President Donald Trump signing a law making it easier for some people with mental illness to buy guns.
Despite repeated requests from CBS News, the White House press office has issued only a one-line response.
Mr Trump last year repealed an Obama-era rule allowing the names of certain people on mental health benefits to be entered into a criminal database.
The controversy follows a shooting by a suspect who had mental health issues.
Nikolas Cruz is accused of using a legally-purchased rifle to kill 17 people at his former high school in Parkland, Florida, on Wednesday.
In a tweet, Mr Trump called the gunman "mentally disturbed" and vowed to "tackle the difficult issue of mental health" during a speech to the nation.
But the Republican president's critics noted his own annual budget proposed this week would cuts hundreds of millions of dollars in funding for mental health programmes.
So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior. Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!— Donald J. Trump (@realDonaldTrump) February 15, 2018
Why won't White House release photo?
CBS News says it requested a copy of the image - which White House photographers confirm exists - 12 separate times by phone or email.
White House spokeswoman Sarah Sanders has only said in a note dated 19 April 2017: "We don't plan to release the picture at this time."
CBS News asked the White House again on Thursday to release the photo, but has not received a response.
Legislation is often signed into law with much fanfare at the White House, including photo-ops, press conferences and even gifts to selected participants.
Mr Trump has boasted of having signed into law "more legislation than anybody" - a claim fact checkers say they have debunked.
What was the law Trump signed?
HJ Resolution 40 was signed by President Trump on 28 February last year, weeks after his inauguration.
It repealed an Obama-era rule that would have affected about 75,000 US citizens who are too mentally ill to handle their own disability benefits.
The Obama measure covered those of "marked subnormal intelligence, or mental illness, incompetency, condition, or disease".
It also ordered the US Social Security Administration, which administers benefits, to add these names to the National Instant Criminal Background Check System.
That database is used by the FBI to determine who is able to purchase a firearm.
The National Rifle Association, an influential gun lobby, was not the only opponent of the Obama-era gun control measure.
The ACLU, a prominent civil-rights organisation, and mental health advocacy organisations backed the repeal that was signed by Mr Trump.
Analysis by Anthony Zurcher, BBC Washington
Donald Trump likes to tout how many laws he's signed - even if some are no more significant than naming a post office or appointing a member of an advisory board. There's one bit of legislation the White House seems keen for Americans to forget, however.
The repeal of an Obama-era rule requiring the Social Security Administration to provide information about individuals with mental health issues for gun-purchase background checks is a bit more complicated than Mr Trump's critics make it out to be.
Civil libertarians and disability rights activists had serious reservations about the potential for privacy violations and a chilling effect the rule might have on those who need counselling services.
What's worth noting, however, is that the White House - with its reluctance to provide evidence of the bill-signing - is acknowledging this could be damaging for them. Presidential strategists probably envision photographs of the event in countless Democratic campaign adverts.
The president reportedly told aides after Parkland that they have to "do something" in response. The White House's reluctance to own up to its only legislative action on firearms is another indication that, when it comes to gun control, they may feel the ground shifting beneath their feet.
What's the reaction?
Late night comedian Jimmy Kimmel, who has often used his show as a political platform, excoriated Mr Trump for signing the bill.
"You've literally done nothing," on guns, Kimmel said tearfully on Thursday.
"Actually, you've done worse than nothing. You like to say this is a mental health issue.
"One of your very first acts as president, Mr Trump, was to roll back the regulations that were designed to keep firearms out of the hands of mentally ill," he continued.
"So I agree, this is a mental illness issue, because if you don't think we need to do something about it, you're obviously mentally ill."