Even as a global crackdown on secretive tax havens has gathered pace, Panama, an entrepot of offshore finance, has remained a stubborn holdout.
But a huge data leak from one of the country's top law firms, Mossack Fonseca, and reports that it helped hide billions of dollars in assets for global politicians, sports stars and entertainers will test its resolve to resist a worldwide push for transparency.
"There will be political pressure and commercial pressure," said Mr Pascal Saint-Amans, the top tax official for the Paris-based Organisation for Economic Cooperation and Development.
Panama's offshore specialists have long been used by some of the world's biggest companies to hold foreign investments tax-efficiently. But the country has also acquired a reputation for opacity. Companies incorporated in Panama were more likely to appear in the World Bank's database of big corruption cases, published in 2010, than those of any other country except the US and the British Virgin Islands.
Panama was already facing international criticism after it emerged as the only significant financial centre to refuse to adopt new international transparency rules in February. The rules were introduced by the G-20 after the US took the lead.
The groundswell of support for such rules was partly a result of public anger over tax evasion following the 2008 financial crisis.
Under the new rules, an unprecedented transfer of tax information will begin next year, easing attempts by authorities to prise open previously secret offshore accounts.
Panama is one of just four jurisdictions, along with Bahrain, Nauru and Vanuatu, that have refused to sign up.
One industry expert said that Panama's refusal would force banks in other jurisdictions to do detailed due diligence on any entities they are doing business with in Panama. Some banks were likely to decide that the extra costs and regulatory risks are not worth it, he said.
Ms Fiona Fernie of Pinsent Mason, an international law firm, said: "There are a number of banks withdrawing from offshore jurisdictions. They are risk- assessing their business models and where they do business."
The French government has already threatened Panama over transparency, saying in December that it would be put on a list of non-cooperative jurisdictions if it did not make rapid progress in responding to a request for assistance from French authorities. In a statement issued yesterday, France said it had reiterated its determination to see Panama comply with international rules on tax transparency in February.
European Parliament lawmakers have jumped on the revelations as evidence of the need for tougher European Union (EU) regulation of the use of shell companies and trusts to conceal wealth.
The European Commission last year published a list of offshore tax havens, incurring furious reactions from those, including Panama, that were named. Officials removed it from the EU's website after several months, saying further work was needed on the methodology.
Brussels at the end of 2014 agreed that nations should compile registers that identify the true owners of shell companies, and so in theory lift the veil of secrecy on offshore accounts. Countries have until June next year to set them up. But the commission is seeking to bring that deadline forward to the end of this year, as part of a push to tackle money-laundering and terrorist-financing.
Panama has already made some changes in response to criticism from the Financial Action Task Force (FATF), the international financial crimes watchdog, which put the country on its "grey list" of anti-money-laundering, high-risk countries in June 2014. It was removed in February after the FATF said it recognised Panama had "made significant progress" in improving its regime to combat money laundering and terrorist financing.