It's a theme familiar to students of American history – a group of single-minded Texans taking a stand at the Alamo. But a gathering on Saturday at one of the country's most symbolic national monuments has its roots in an altogether more modern fight: the right of citizens to openly carry firearms, against growing calls for more restrictive gun laws.

Organisers of the rally, which is named "Come and Take It San Antonio", have chosen the site of the famous 1836 showdown for a reason. The battered but preserved stone church is where Colonel William Barret Travis and about 200 members of the Texian Army held out for almost two weeks before the vastly superior numbers of Mexican forces overwhelmed them.

"We're doing this to show that we're not going to back down," said Victoria Montgomery, a spokesperson for Open Carry Texas, one of the pro-gun groups behind the protest. "We are going to fight for our rights, and it's not OK for police to just say whatever they want and make up the rules as they go along."

Texas has some of the most liberal gun laws in the country, allowing citizens to openly carry long guns – rifles or shotguns – in public. But San Antonio police have recently arrested activists carrying such weapons, citing a more restrictive city ordinance banning weapons in public places and a section of the state penal code that outlaws the display of deadly weapons in public "in a manner calculated to alarm".

With the approval of some powerful players in state political circles, most notably the land commissioner, Jerry Patterson, and Kathie Glass, a candidate in next year's election for state governor, the protesters fought for and won the right to stage the event at the shrine to Texas liberty.

Demonstrations over other causes have been allowed at the city-owned Alamo Plaza, outside the historic four-acre site which includes the Spanish mission-era church from which Travis wrote his famous "victory or death" letter before he and his fellow defenders were killed. But the decision by Patterson's office to allow Saturday's event, which is organised by a loose coalition of pro-weapons organisations and will feature about 1,000 protesters carrying their guns, to take place inside has triggered furious debate. Patterson himself will be the main speaker at the rally.

"It is a difficult precedent to set on the Alamo grounds. What groups will be given access in the future?" state senator Leticia Van de Putte told the San Antonio Express-News.

Lee Spencer-White, president of the Alamo Defenders' Descendants Association and a relative of George Jennings, a cannon operator in the Texian army who died in the battle, said she was also concerned.

"We certainly consider the Alamo our family cemetery. Our guys died there and we take it very seriously," she said. "Today it's a gun rally. What is it going to be next month, next year?"

Jim Suydam, a spokesman for Patterson's office, denied there was any favouritism in the commissioner's decision to approve the location of the rally, and said he was confident the event in front of the church would pass off peacefully. He said Patterson had insisted on safety measures to prevent the accidental discharge of weapons, including the use carry straps and chamber blocks, and that extra Texas Rangers would be on duty.

Meanwhile, San Antonio's police chief, William McManus, downplayed recent emotions in the debate. Tempers boiled over in August when his officers charged three local men with disorderly conduct after they were arrested outside a city Starbucks wielding rifles and wearing camouflage clothing, an episode that prompted allegations of harassment.

"We'll have plenty of police officers visible out there in hopes that will ease anyone that was fearful of people toting around weapons," McManus said. "This isn't an us-versus-them."