One of the gun control signs that were displayed on Clear Channel billboards before the company pulled them down  Thursday. (Stop Handgun Violence/John Rosenthal)

For 20 years, drivers breezing (or crawling) down Massachusetts Turnpike would pass Fenway Park and also a billboard about gun safety.

In the next few weeks, that will change. And efforts to keep the billboards alive elsewhere in the state have hit a roadblock.

This week, the National Rifle Association’s Massachusetts affiliate, the Gun Owners’ Action League (GOAL), successfully pressured two companies to rescind their offers of free, temporary billboard space that would allow the ad campaign to continue its run until it finds a permanent home.

A total of four media companies had “enthusiastically” donated a total of 36 billboards to the cause, John Rosenthal, co-founder of Stop Handgun Violence, told The Washington Post. The biggest donor by far was Clear Channel, which donated 25 billboards.

On Thursday, Clear Channel also became the first to back down on their pledge after gun rights advocates flooded the zone with calls, e-mails and social media messages questioning why the company hadn’t given “equal time” to second amendment advocates.

“We support many nonprofit and government campaigns to benefit Boston in areas including education, the environment, diversity and more; we also respond swiftly to crises with weather notifications, AMBER alerts and support for law enforcement in cases like the Boston Marathon bombing,” the company wrote in a statement. “With others in the community, we lent media to an anti-violence message. This campaign has become politicized and misconstrued as a political position by our company, so we have taken it down.”

Hours later, Logan Communications, which had also initially agreed to donate free billboard space, said they could only move forward with the agreement if the billboards were paid for, Rosenthal said.

Gun rights advocates have abided by the gun safety message touted on the massive 252 foot ad for years — but just barely. In reality, they couldn’t do much about it.

The billboard had been located on a parking garage adjacent to the Massachusetts Turnpike privately owned by Rosenthal, who only recently sold it to the owners of the Boston Red Sox.

“Any person who’s 20 to 30 years old has only known Boston with this billboard,” Rosenthal said.

One of the billboards featured on a building owned by Rosenthal until recently. (Stop Handgun Violence/John Rosenthal)

Until a new location is constructed, Rosenthal planned to rely on donated billboard space to fill the gap.

A gun owner himself, Rosenthal said that the message of the billboards is anything but controversial.

“We’re not anti-gun, we’re pro-life,” the new signs will say. “Massachusetts gun laws save lives.”

The media companies who donated billboard space “all embraced it,” Rosenthal said.

“They were proud of the success. Massachusetts has proven you can enact reasonable gun laws and have dramatic success,” he added. “And that emessage was so moderate. We support gun rights, we support life. There was nothing controversial about it to the billboard companies.”

Initially, Clear Channel seemed eager to participate.

“When we realized he would no longer have his . . . billboard to get out the message about gun control, we offered to utilize some of our space,” Stephen Ross, president of the Boston division of Clear Channel Outdoor told the Boston Globe. “It was easy for us to make a huge impact on such an important message.”

The sudden about-face makes this victory even more sweet for gun rights advocates, if only because it puts a small but notable dent in Rosenthal’s groups’ 20-year run promoting gun control policies in the state.

“The message being broadcast for Mr. Rosenthal, at no charge by the companies, provides inaccurate, discriminatory, and misleading information, which will do nothing to bolster firearms safety or prevent crime,” said Jim Wallace, executive director of GOAL in a statement.  “Our first thought was, is this a joke?  Because the messaging certainly does not reflect reality.”

“If the billboard companies were really interested in saving lives they would grant space to GOAL.  We have a proven record of providing gun safety and legislative solutions that work,” he added.

Rosenthal said that two other companies, Total Outdoor  and Outfront Media, have since confirmed to him that they stand by their initial pledges. Ross of Clear Channel declined to comment to The Post beyond the company’s written statement, and calls to Logan Communications have not yet been returned.

Rosenthal said, however, that the president of Boston’s Clear Channel outdoor division apologized for walking back the company’s pledge.

“He was sorry,” Rosenthal said of his conversation with Clear Channel’s Ross. “He totally underestimated what kind of response the extreme gun lobby would have and it caught him off guard.

One of the gun control messages featured on a billboard overlooking Massachusetts Turnpike in Boston. (Stop Handgun Violence/John Rosenthal)