"We are already in court in New York and we will be in court and aiding those in Maryland -- and I am myself a Maryland resident -- who want to challenge the constitutionality of this and other provisions here in Maryland," Keene told The Baltimore Sun.
Maryland's General Assembly last week passed the law that prohibits the sale of 45 kinds of military-style semi-automatic rifles and includes other strict provisions.
Keene said it is unconstitutional to ban commonly used guns and one of those banned by the new law is the AR-15, which is the nation's best-selling rifle.
Mdpetitions.com, a group that forced three Maryland laws to referendum last year, tentatively plans to ask the state Board of Elections to bring the new gun law before voters, said Neil Parrott, the group's founder and Republican member of the state's House of Delegates. He said the group has not yet formally decided whether to petition for a ballot-box battle, but it wants to have a petition created by next week as a possible first step.
Maryland's new law is among the strictest passed in any state legislature since Sandy Hook Elementary School massacre in December in Connecticut that left 20 children dead. The law prohibits the AR-15 rifle that officials said was used in the shootings.