The petition requested "an in-depth public consultation period on changes to New Zealand firearms legislation, to ensure effective firearms legislation reform that does not unduly punish law-abiding firearms owners while maintaining assurances of public safety".
It called the Government's gun law reforms "ill-advised, partly due to the speed at which they have been implemented and also due to (understandable) emotionally driven public pressure".
The Gun City email, obtained by the Herald, asked for more information on the Government's proposed buy-back scheme, including whether it would compensate for gun accessories and ammunition, lost income or employment, booked travel to events to use MSSAs, or losses from investment in shooting facilities.
It also called for an independent inquiry into how the gunman in the Christchurch shootings obtained a firearms licence.
"The reasons and activities for which we own guns vary. Let's stand united as Firearms Licence holders rather than dividing into different groups, in the hope that other shooting disciplines will not be affected," the email said.
It asked subscribers to write to MPs, police, and media, and included a link to a Council of Licenced Firearms Owners document to help people prepare submissions.
The linked document contained phrases such as, "You are confiscating my property from me and I am not being given a chance to have any say about it", and "I do not like the way I am being treated. I have not done anything wrong. I am law-abiding."
Act Party David Seymour has also criticised the "rushed process" of the legislation and said it would "deny the public the chance to have their say".
He said it could lead to legislation that failed to solve the problem.
"Trying to pass a law in less than three weeks is a recipe for bad lawmaking."
Gun City boss David Tipple, when contacted by a Herald reporter, asked whether the reporter thought there was a legitimate use for an AR-15 - which was used in the Christchurch attack - in society, and then hung up.
Tipple has previously confirmed that Gun City had sold four weapons to the accused gunman in a police-verified, online process.
There are 13,500 known MSSAs in New Zealand, and an estimated 1.2 million to 1.5 million firearms overall.