A war of words over words erupted this week as gun rights advocates checkmated Boston developer John Rosenthal’s effort to spread his anti-gun violence message across Massachusetts via billboards.

The billboards, which say “We’re Not Anti-Gun. We’re Pro-Life. Massachusetts Gun Laws Save Lives,” feature a Bushmaster XM-15 assault rifle with a white surrender flag in the barrel.

The Northborough-based Gun Owners’ Action League and the National Rifle Association helped lead an offensive against Boston’s Clear Channel Outdoor, one of several local companies that donated billboard space to Stop Handgun Violence, a group that Rosenthal co-founded to promote stronger gun laws and gun safety.

Clear Channel decided to take down the billboards after gun rights advocates flooded iHeartMedia, the company’s San Antonio-based corporate parent, with emails and phone calls threatening a nationwide boycott if the firm did not pull out of the campaign. A company spokesman told the Boston Globe that the offer of the billboard space to Stop Handgun Violence had been “misconstrued as a political position by our company, so we have taken it down.”

Rosenthal decried Clear Channel’s decision. “The gun lobby doesn’t want a rational discourse on responsible and effective gun laws,” he said in a statement.  “In fact, it wants to stifle any discussion at all about gun safety laws. It wants to control how we think about guns, how we speak about guns, and how we debate the issue of guns.”

Jim Wallace, the Gun Owners’ Action League’s executive director, said the billboards are “deceptive.” He claims that state Department of Public Health figures indicate that gun-related homicides and assaults have significantly increased since the late 1990s.

Stop Handgun Violence has argued that Massachusetts gun deaths alone have dropped 63 percent since 1994.

“[Rosenthal] has a First Amendment right to say what he wants, but we also have the right to react to what he’s saying,” Wallace.

The gun rights group plans another round of pressure tactics if Rosenthal decides to pay for billboard space.

“If the companies decide to take a paid ad that says the same lie, then I’m sure that our organization will take a hard look at that and probably ask our members to do similar things that they’ve been doing now,” Wallace said.

The group has no plans to talk with Rosenthal. “There’s really no having a rational conversation with John about this stuff,” Wallace said.

Billboard companies donated the space to Rosenthal, who has to take down a massive billboard over the Massachusetts Turnpike near Fenway Park which has displayed anti-gun  violence messages for more than 20 years. He sold the garage to the Boston Red Sox in 2013 and, under terms of the sale, had to take down the billboard this month.

The developer plans to install another large anti-gun violence billboard on Fenway Center, his $450 million mixed-use development currently under construction over the Turnpike.  Rosenthal expects to complete the project in 2018.