"We've never seen growth like that in 30-plus years of monitoring groups on the radical right," said Mark Potok, a senior fellow at the center in Montgomery, Alabama, who co-authored the report.
The report warns of the potential for more violence, like the recent killing of two Las Vegas police officers by a pair of anti-government zealots Jerad and Amanda Miller who spent time at Bundy's ranch before they were asked to leave because of their extremist views.
"Government officials need to understand what motivates this movement because the Millers will not be the last to demonstrate their anti-government rage with bullets," said the report entitled "War in the West, The Bundy Ranch Standoff and the American Radical Right."
The BLM says Bundy owes over $1 million in grazing fees and penalties for trespassing on federal property without a permit for more than 20 years. Bundy, whose ancestors settled in the area in the late 1800s, refuses to acknowledge federal authority on public lands.
The bureau backed down during the showdown with Bundy and his armed supporters, citing safety concerns. Bundy's allies subsequently released the 380 cattle collected during a weeklong operation from an arid range half the size of Delaware.
Among other things, the report praised U.S. Attorney General Eric Holder's recent revival of the Domestic Terrorism Executive Committee. It also calls for the criminal prosecution of those who pointed weapons at law officers at the Bunkerville ranch.
Bundy said Thursday he hasn't seen any evidence that any protesters pointed guns at law officers and he hasn't had "any problem with law enforcement" since he recovered his cattle.
"We don't have BLM shutting off our roads or trying to steal our cattle. So in that sense, things are good better than it has been in a long time. We're producing beef on this old desert range right now," he told The Associated Press by telephone. He also questioned why the SPLC spent the time and money to produce the report.
"They don't have any rights on this Nevada land," Bundy said. "It seems they just wanted to stir something up, make something bad that has been really good."
Report co-author Ryan Lenz, who was at the Bundy ranch during the standoff, said Bundy and his allies took great pride in turning back the BLM. He said the agency fueled the antagonists by sending in agents with riot gear, helicopters and dogs.
BLM spokeswoman Celia Boddington said the agency was reviewing the report but had no immediate comment.
The report cites a number of political leaders who called Bundy a "hero" in the aftermath of the showdown, including Janine Hansen, a longtime Nevada libertarian who is running for Congress as a candidate for the Independent American Party.
Hansen said in an email to AP on Thursday that the law center is a "radical leftist" organization.
"Any criticism they have for me I consider a compliment for my effectiveness in fighting for freedom," she said.