A trial to decide who should pay for the rising costs associated with the coronavirus pandemic is about to start in London.

The UK financial regulator took Europe’s largest insurers to court in a case that starts Monday to establish whether they should pay out pandemic-related claims. Hiscox Ltd., RSA Insurance Group Plc, Zurich Isurance Group AG and five other companies will represent the industry at the eight-day trial.

A ruling against the insurers could mean tens of millions of dollars in additional claims, hitting a sector that is already facing its biggest test to date. Lloyd’s of London, the world’s largest insurance exchange, estimated the global pandemic could cost insurers more than $200 billion.

“Critically, where any policy wording is ambiguous, the court will interpret it against the insurers,” said Sarah Jane Mahmud, an analyst with Bloomberg Intelligence.

The trial is one of a number of global cases over business interruption claims. AXA SA, France’s largest insurer, was ordered by a court to pay a Parisian restaurateur two months of lock down-related revenue, and the firm has since agreed to cover losses sustained by several hundred cafes during the shutdown.

Insurers didn’t respond to requests to comment ahead of the hearing.

The Financial Conduct Authority brought the UK case on behalf of aggrieved policyholders, and the court decision would also affect more than 20 other insurers including Allianz SE, American International Group Inc., and Chubb Ltd.

Policies held by around 370,000 policyholders could be affected by the case.

“We have moved at pace to bring this action to court to provide clarity for insurers and policyholders,” the FCA said in a statement. “The start of the court proceedings marks a significant step forward in the process.”

The so-called test case will hinge on whether the terms of small business owners’ policies give the insurers a loophole. There are disputes on a number of different wordings, including whether physical damage needs to be sustained in order for payouts to be warranted and how close a coronavirus case has to be to the business for an insurer to make good on a claim.

Even if the FCA wins, some policyholders may “face challenges from insurers when it comes to proving and quantifying their loss,” said Samantha Holland, head of insurance at law firm Gowling WLG in Birmingham, England.

Lawyers for Hiscox and other insurers are set to argue against paying out fully on claims made by businesses forced to shut because of the pandemic, saying that shops in Sweden lost money even without a strict lockdown and UK firms would have lost out similarly.