Keir Bloomer, president of the Association of Directors of Education, said the report's proposals would "seriously disturb existing differentials".
"The key issue is whether we can persuade other local authority staff that the situation facing teachers and the changes they are required to accept are so exceptional that exceptional treatment is necessary in pay terms," Mr Bloomer said.
McCrone proposes that the new maingrade scale for teachers shoul extend within two years to pound;34,850, while heads would earn up to pound;63,038.
"The answer is either to pay those managing them more or alter the position so that the relationship changes and they are not managed in the same way as at present," Mr Bloomer said. Many heads still looked to education officials for detailed guidance. "If that was to alter, it would be a fairly significant change."
Many FE principals would earn less than some heads. The most recent figures showed college principals were paid between pound;43,000 and pound;85,000.