More than a third of requests for supply staff are going unmet in Scottish schools, according to a council report.
Around 36 per cent of requests for supply cover are not being met in East Lothian primaries, with a similar situation reflected nationally, says a report that went before the council's education committee this month.
Securing cover in secondary schools is also difficult, it states.
The authority plans to "boost" supply teacher numbers by offering teachers on part-time contracts the opportunity to join the supply list.
At present, 225 staff are on the list but only 72 are active, the report states. Many of them refuse to provide cover on certain days, travel certain distances or accept short-term placements.
Short-term supply teachers' pay was halved in the last teachers' agreement, two years ago.
Most heads were struggling to find supply cover for most subjects, said Ken Cunningham, general secretary of School Leaders Scotland.
"Reducing supply cover wages to their current levels was both terribly short-sighted and hugely damaging to the standing of the profession," he said. "We are now reaping what was sown."
The supply shortage was "a growing problem", said Greg Dempster, general secretary of the primary heads' and deputes' union, AHDS.
An improved pay deal for short-term supply teachers could come out of the continuing pay and conditions talks taking place at the Scottish Negotiating Committee for Teachers. Thus far, however, this is understood to have been one of the main sticking points.
Original headline: One third of requests for supply teachers left unmet