Membership: 10,000, mostly in vocational and community schools. Also well represented in the booming institutes of technology.

Style of union: Left-leaning union with high tolerance level for dissidents. Its general secretary, Jim Dorney, is regarded as a shrewd figure who gives the radicals their say - and still controls the agenda.

Pay strategy: Voted against the PPF but rowed in when the Irish Congress of Trade Unions backed the deal at a special conference earlier this year.

ASTI action has given a new impetus to the anti-PPF group within the TUI. Now threatening to ballot members on industrial action unless Government moves to compensate members for inflation.

Leadership remains confident that PPF review plus new benchmarking timetable will sort out the pay problems. However, a large grouping within the union is now ready to support more militant action if the Government does not deliver.