The National Rifle Association (NRA) is suing Florida to block new gun-control laws in the state.
The gun lobby filed the lawsuit hours after Governor Rick Scott signed the far-reaching bill, the culmination of three weeks of lobbying by survivors of the worst school shooting in 20 years.
While the legislation falls short of achieving the ban on assault-style weapons like the one used in the shooting, a move sought by survivors, it does raise the legal age of buying rifles in Florida to 21.
The bill - dubbed the Marjory Stoneman Douglas High School Public Safety Act - also extends a three-day waiting period for handgun purchases to include long guns and bans bump stocks, which allow guns to mimic fully automatic fire.
It also creates a so-called guardian programme which allows provision for teachers to arm themselves.
The NRA said the measure "punishes law-abiding gun owners for the criminal acts of a deranged individual".
In a statement Chris W Cox, executive director of the NRA's Institute for Legislative Action, said: "If we want to prevent future atrocities, we must look for solutions that keep guns out of the hands of those who are a danger to themselves or others, while protecting the rights of law-abiding Americans."
The new gun control measures follow an extraordinary three weeks of lobbing in response to the mass shooting at the Marjory Stoneman Douglas High School on Valentine's Day where 17 people were killed.
Signing the bill, the Republican governor said the bill balances "our individual rights with need for public safety".
He told the students who had quickly become the public face of the gun-control movement in the wake of the tragedy, "you helped change our state. You made a difference. You should be proud."
"It's an example to the entire country that government can and has moved fast," said Mr Scott, whose state has been ruled for 20 years by gun-friendly Republican lawmakers.
Tony Montalto, whose daughter Gina was killed in the shooting, read a statement from victims' families: "When it comes to preventing future acts of horrific school violence, this is the beginning of the journey. We have paid a terrible price for this progress."
Student activists from the school called it "a baby step".
"Obviously, this is what we've been fighting for. It's nowhere near the long-term solution," said Chris Grady, a senior at Stoneman Douglas High.
"It's a baby step but a huge step at the same time. Florida hasn't passed any legislation like this in God knows how long."
The 19-year-old suspect Nikolas Cruz has been charged with 17 counts of first-degree murder over the Valentine's Day massacre.