A teacher in Orkney can be promoted to the post after five years but only after 10 in Shetland and Falkirk. The average for councils with restrictions is seven to eight years but 20 authorities have no barriers, according to a survey carried out by the Scottish Tories.
Brian Monteith, the party's education spokesman, said it should be left to heads to decide who should be recommended for a senior teacher's post without local authority interference.
"Why should a teacher have to serve 10 years in one authority yet only have to serve five in a neighbouring one? Local authority restrictions are not necessary. If a teacher has demonstrated the qualities to gain promotion to an administrative post after only four years, then surely the alternative of a senior teacher post should be made available," Mr Monteith said.
The post was introduced by the Conservative government in 1988 to provide an attractive salary grade that would keep ambitious teachers in the classroom, Mr Monteith said.
The Tory manifesto will highlight the need for increased powers for headteachers.
All 32 councils were surveyed. East Lothian, Dumfries and Galloway, Glasgow and South Lanarkshire declined to take part.