A security firm is under investigation for allegedly supplying cloned badges to unlicensed stewards at UK festivals this summer.
The Security Industry Authority (SIA) confirmed it was investigating LS Armour Security Ltd of Barry, south Wales, following a compliance check.
The watchdog issues licences to bouncers and security firms.
It said it was "exceptional" for it to comment and had taken "unprecedented action due to public safety".
The inspection has led to two arrests and the seizure of business records, including some relating to future events with contracts for security operatives around the UK.
The SIA has also written to various organisers of events and festivals that have used the firm in the past and have bookings in the future.
In a statement, an SIA spokesman said: "This type of unlawful conduct remains rare due to responsible organisers and security providers conducting appropriate due diligence.
"Nevertheless, the SIA understands that at this time of year, event organisers and primary contractors may not have sufficient SIA-licensed staff, which can lead to extensive sub-contracting.
"This provides opportunities to rogue providers that, with appropriate checks by organisers and primary contractors, can be largely mitigated."
In a letter to promoters, the SIA's deputy director said: "If SIA-licensed staff arrive on site and are unknown to you, you must take all reasonable steps to ensure the person named on and in possession of the licence are the same person by requiring them to provide further evidence of identity.
"This will mitigate the risk of the cloned licence."
In response to the report, LS Armour Security Ltd's director Erica Lloyd told the BBC: "As a company we have only been made aware of one arrest as a result of a cloned badge, and this individual was cautioned by police and subsequently released without charge.
"At this point this individual was contacted by LS Armour and told he would no longer be employed for any future events."
She said that the SIA's system to check whether someone holds a valid licence - the Register of Licence Holders, available on the SIA website - was "simplistic" and "inadequate".
She added that this view was "brought to the attention of an SIA representative earlier this month, although at this time and on looking at the SIA website this appears to still be the only avenue of checking available".
Ms Lloyd said LS Armour Security Ltd were "fully complying with the SIA investigation".
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