The Night Time Industries Association (NTIA) has accused Hiscox underwriters of saying that the company would "positively respond" to coronavirus claims, just days before the lockdown was announced.
The insurance firm has come under fire for refusing to pay out business interruption claims, with the NTIA among several groups pursuing claims against it.
Michael Kill, chief executive of the NTIA, said: "We continue to see frustration from policyholders across the sector. We have been approached by a substantial number of claimants for advice and support, who have received communication from Hiscox denying their claims.
"We have found evidence that suggests even their own underwriters were discussing how the cover would positively respond only days before the lockdown happened, leading to clients renewing with them and not taking options of cheaper policies elsewhere.
"Hiscox have underestimated the response from the industry, and the claimant's willingness to ensure that each disputed claim is challenged.
"While we focus on the campaign to challenge Hiscox Insurance on the disputed claims, we must also take account of the crisis that has created this situation and build towards working with the wider insurance industry to future-proof cover for our sector."
A spokesperson for Hiscox said: "We understand these are incredibly difficult times for businesses and we are paying claims that are covered by the policies we issue fairly and quickly. We review every case individually, and if any customer has concerns about the application of their policy, we encourage them to get in touch with us directly.
"Where the application of a policy is disputed, our focus is on helping to provide customers with greater certainty. A fair and fast resolution is in everybody's interests, which is why we will work with the UK insurance industry, our regulators and customers to seek an expedited resolution through the range of existing independent mechanisms."