Up to 200 English charities are likely to be required by the Office of the Scottish Charity Regulator to amend their constitutions to comply with a section in the Scottish charity law of 2005.
The regulator says differences in the definition of charitable purpose in recent Scottish and English law mean problems could arise in the case of charities whose constitutions include a general power for property to be used for purposes defined as charitable under English law.
It says this could lead to their assets being used for purposes not defined as charitable in Scottish law. For example, the latest English law says the promotion of the efficiency of the armed forces is charitable, but Scottish law does not.
Stephen Lloyd, head of charities at Bates, Wells & Braithwaite and former chair of the Charity Law Association, described the requirement as "madness", especially because the Scottish Parliament had promised "light touch" regulation.
He said it would cost most charities at least £500 plus VAT to alter their constitutions, and there would have to be an Order in Council in the case of organisations established by the Privy Council, such as the British Red Cross Society.
Lloyd has complained to the Charity Commission, the Office of the Third Sector and the Better Regulation Task Force.
A spokesman for the Scottish regulator said it was applying the requirement flexibly. "We're being as helpful as we can," he said.