The 11-page lawsuit goes directly after the Connecticut General Assembly and Governor Dannel Malloy.
The National Shooting Sports Foundation said state lawmakers bypassed the normal legislative process when crafting the massive gun violence bill.
"The process was very unfair, very rushed and violated state law," Larry Keane, NSSF general counsel, said.
The lawsuit argues that lawmakers improperly used what's called emergency certification to push the bill through. E-cert is a process commonly used which bypasses the normal public hearing process. The gun group said there was no emergency.
"The only emergency that existed here was a political one," Keane said.
Since e-cert was used there was no public hearing after the bill was filed. There were multiple hearings, well attended by gun owners, before the legislation was written.
"There was a bipartisan commission set up by the legislature and they held hearings but there was no legislative text," Keane said. "We are very disturbed by the law. We are very disturbed by the process."
Senate President Donald Williams was quick to respond. He said this is part of a shameful national campaign to intimidate legislators.
"The gun manufacturers that support the NSSF apparently believe that the murders at the Sandy Hook Elementary School were not worthy of emergency-certified legislation after extensive public hearings and meetings," Sen. Williams said.
This is now the third lawsuit to be filed challenging the law which was signed on April 4. NSSF, which is located just three miles from Sandy Hook School, is not challenging the law's Constitutionality. Supporters of the law believe that is significant.
"They came away with the opinion in my opinion that all of these measures that were passed comply with the Second Amendment," Monte Frank, Sandy Hook parent and member of Newtown Action Alliance, said.
Frank, who is also an attorney, is confident that the law will be upheld.
"They are trying to maximize the sale of guns," he said. "That's their job. Unfortunately they're here."