Visitors to Houston Zoo can now pack a little something extra besides a camera and picnic basket. The institution has lifted its longtime firearms ban amid a broader push by gun-rights advocates who are pressuring zoos in Texas and elsewhere to do the same.

Gun-rights supporters say publicly owned zoos have misinterpreted laws and are illegally posting signs that ban firearms. Some zoos have countered calls for policy changes by claiming they are considered amusement parks or educational institutions – venues that legally can enforce gun bans in many states.

An advocacy group in Texas is singling out zoos under a new state law allowing complaints about unlawful gun restrictions to be forwarded to the state’s attorney general for potentially steep fines. Similar efforts have occurred elsewhere, including in Missouri where St Louis Zoo went to court to prevent an Ohio man from bringing a gun to the zoo to test its no-weapons policy.

“I am not anti-zoo,” said Edwin Walker, of Texas Law Shield, the group that recently filed complaints against Houston and Dallas zoos.

Americans remain bitterly divided over the question of gun laws. Gun control advocates say a series of mass shootings proves the need for tighter regulations on purchasing and carrying weapons. But many argue just the opposite, saying citizens should have the right to carry firearms in public places to defend themselves.

Many zoos do not allow guns on the premises. But laws vary from state to state. In Kentucky, a 2012 revision to state law permits people to carry firearms openly into facilities owned by municipalities, such as libraries, parks and zoos.

The Houston Zoo has already felt a backlash after the city ordered it to take down its no-gun signs. Parents and children gathered last month to greet zoo visitors with warnings about the policy change, with some holding signs such as “Hey Gun Lobby, quit monkeying around!”.

A zoo spokeswoman said it was reviewing legal options in light of evolving gun laws. Officials previously believed they could ban firearms because they offered an “educational attraction” for children and others.