In a federal court, the NRA, the most influential anti-gun control group in the United States, accused Florida of violating the US Constitution.
"We filed a lawsuit against the state for violating the constitutional rights of 18- to 21-years-old," said Marion Hammer, a lobbyist for the NRA in Florida.
The NRA added that the blanket ban violates the fundamental rights of thousands of Florida citizens and is thus invalid under the Second and 14th Amendments.
Final passage of the bill by state lawmakers came about three weeks after the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, which killed 17 people and injured 14 others.
The bill, the first major gun-control state law in Florida in decades, narrowly passed the state Senate in a 20-to-18 vote on Monday before sailing through the House of Representatives on Wednesday in a 67-50 vote. Both the state House and Senate are controlled by Republicans.
"I am going to do what I think are common sense solutions," Florida's Governor Rick Scott said after the signing.
"I have not spoken to anybody in the NRA since this happened," said Scott, who previously received an A-plus rating from the NRA.
Meanwhile, he criticized the inaction in the White House and Capitol. "If you look at the federal government, nothing seems to have happened there," he said.
Currently, the US Senate has no gun control bill scheduled for debate, and the only measure moving in the House of Representatives is a bill seeking for more training for students and teachers to address school shootings.
According to the new Florida state law, the buyers need to wait for three days before receiving a firearm in most cases.
The new measures also include banning the sale of bump fire stocks that can make semiautomatic rifles perform like fully automatic ones, investing 400 million US dollars in improving mental-health services and boosting physical security of school buildings, as well as a controversial "guardian" program to train and arm some voluntary school personnel.
The legislation also excludes proposals to ban assault weapons like AR-15 assault-style and other semiautomatic rifles.
On Wednesday, Nikolas Cruz was formally indicted on murder charges over the Parkland shooting on Feb. 14.
Cruz, who is 19 years old now and purchased his gun at 18, had a history of mental issues, numerous encounters with police and was expelled from school last year for disciplinary problems, said authorities.