The world's biggest asset managers are pressing European Union regulators for extra time to adjust to new regulations that could upend about 80 billion euros (US$91 billion) of money-market funds.

The fund companies and their trade association say more time is needed because it has become clear only in recent days that a common industry practice will no longer comply with the rules as overseen by the Central Bank of Ireland, one of the main regulators for fixed–share-price funds. BlackRock Inc. and the asset-management arms of JPMorgan Chase & Co. and Goldman Sachs Group Inc. are among the biggest managers of the funds, and will need to adjust their euro-denominated funds by as early as Jan. 21, when the rule takes effect.

See also:

• Money Fund Giants Brace for $94 Billion Hit from EU Rules

BlackRock is calling for a transition period to help the market adjust, and said in a statement that its board overseeing money-market funds in Europe is preparing a contingency plan for regulators. Corporate treasurers around the world rely on money funds to park their cash with the assurance they'll be able to take out every dollar—or euro—when they need funds for payroll or investments.

The Institutional Money Market Funds Association, which represents the fixed–share-price fund industry, said it was disappointed in the EU's decision to ban a tool called the reverse distribution mechanism that the industry has used in recent years to keep share prices fixed even while yields on securities in Europe have been in the red. Jane Lowe, the association's secretary general, said the industry needs at least a year to make the shift.