Earlier this month, a Government-backed report on the future of school qualifications recommended making new professional qualifications compulsory for those wanting to become head teachers.
Currently, many school staff seeking a management role study for the existing Standard for Headship qualification either before they apply or after their appointment, but it is not compulsory.
Unions representing head teachers said the new requirements – to be introduced in five years – would have to be introduced carefully to ensure they did not act as a barrier to people seeking headships.
Ken Cunningham, general secretary of the School Leaders' Scotland union, which represents secondary heads, said: "Any leadership development should not be a barrier to progression, but should be about enhancing the capabilities of future leaders.
"We don't want an absolutely definitive statement about what you should achieve before applying to become a head teacher.
"If you make achieving the qualification too rigid then that runs the risk of putting people off, and we are struggling as it is to get good people in post."
Greg Dempster, general secretary of the Association of Headteachers and Deputes in Scotland, which represents primary heads, added: "The leadership role in education is absolutely critical and we would support the introduction of a qualification for all that improves headship.
"However, the mechanism very much needs to be in place so that it does not become a barrier to getting people into headship. The time deadline is five years so they would need to have a qualification established and enough candidates coming through it to allow there to be competition still for head teacher roles.
"You would have to have considerably more people coming through the qualification than there were actual vacancies."
Dr Alasdair Allan, the Minister for Learning, said any new qualifications would be developed in partnership with the head teachers' unions.
"We need to make sure any qualification is developed in consultation with the profession, and that will happen," he said. "There is no clear delineation of how it will be developed and it is not a question of trying to undermine the position of existing heads or putting off those who want to become a head teacher.
"The success of schools depends on good leadership and we want to make sure people coming into the role do so with confidence."
Concern over a "crisis of leadership" in Scottish schools has been raised in recent years, with large numbers of heads due to retire. Although the Government argues it is on course to fill the vacancies, head teachers say increasingly difficult working conditions are preventing potential candidates from applying.
In recent months, East Lothian Council even con-sidered parachuting secondary teachers into primary schools as head teachers.
Unions argue increased bureaucracy and changes by councils to the way salaries for senior staff are calculated have contributed to the shortages.
Unions are also concerned leadership succession is under threat because of council cuts to the number of deputes and principal teachers – who often go on to become head teachers.
The Government-backed report Teaching Scotland's Future said: "Within five years all aspiring head teachers should have an appropriate qualification or professional award in leadership, as evidence of meeting the Standard for Headship."