Guernsey's chief minister has warned UK MPs that amendments to the Financial Services Bill are based on "misperceptions" over financial transparency.
The amendments seek to force the islands to make company ownership information public, bringing the Crown Dependencies of Guernsey, Jersey and the Isle of Man in line with the UK and its Overseas Territories.
In the letter, Deputy Gavin St Pier writes the amendments are "based on common misperceptions about registers of beneficial ownership and transparency".
There was no evidence public registers of ultimate business owners, such as the UK's, were any more effective than Guernsey's private model of fighting financial crime, Deputy St Pier wrote.
He also branded the attempt to legislate "without our consent" as going against a "centuries-held constitutional rule".
Backers of the amendment argued tackling anonymous offshore companies was an important tool in the fight against money laundering, tax avoidance and tax evasion.