Since 2011, Police Scotland has had a special unit to provide a consistent approach to policing football matches.
It was set-up after a bad-tempered Celtic v Rangers match and now has 15 full-time dedicated officers and an annual budget of £780,909.
The Football Coordination Unit for Scotland says it takes an “intelligence-led” approach to policing at football.
Supporters groups believe their methods have gone much further than filming fans at matches with small cameras.
Jeanette Findlay, from Fans Against Criminalisation, said: “During the campaign against the Offensive Behaviour Act we had reason to believe on more than one occasion that our communications were being intercepted.
“In addition, we have had a number of young men approached to become informants for the police.”
Sky News submitted a freedom of information request to Police Scotland asking how many applications they had made for a warrant to intercept the content of communications in each of the last five years and whether any related to policing of football matches.
Official figures show that across the whole of the UK 3,007 interception warrants were issued in 2016. Nearly all related to serious crimes such as drug dealing and armed robbery or to national security.
Police Scotland refused to disclose how many of those applications came from Scotland, saying: “Detailed information regarding existing and future applications would ultimately reveal specific operational activity.”
They added that it would specifically compromise the tactical advantage of Police Scotland in relation to criminality associated with national security.
Sky News also asked how many communications data application forms had been completed by officers working with the Football Co-ordination Unit in each of the last five years.
This is the form police must submit to check the text messages on someone’s phone or see which websites they have visited.
Police Scotland also refused this request, saying: “It simply cannot be in the public interest for Police Scotland or any agency to confirm the existence of information relating to specific police tactics.”
National security was again used to justify the decision: “The threat of terrorism cannot be ignored. It should be recognised that the international security landscape is increasingly complex and unpredictable.
“The UK faces a sustained threat from violent terrorists and extremists.”
Ms Findlay says the public should be very concerned.
“People should remember that we are not talking about organised crime or terrorism – we are taking about football fans – and yet tactics more suited to such serious criminal activity are being used against us and exemptions to freedom of information requests relevant to national security are used to block legitimate journalistic enquiry into the policing of football,” she said.
The UK’s most senior police officer with responsibility for football is currently leading a review of policing at matches in Scotland. It was ordered after a crush at Celtic Park on 2 September, in which five supporters were injured.
Deputy Chief Constable Mark Roberts will look into intelligence gathering as well as operational planning for games.
Labour MSP James Kelly, who led the campaign in the Scottish parliament for the repeal of the Offensive Behaviour at Football Act, wants to see a change in the culture of policing.
“The review being conducted into policing at football in Scotland needs to produce a step change in police attitudes,” he said.
“Treating football supporters with respect should be a central aim of this review.”