The last recruitment event of this year’s hiring season takes place Wednesday, as the number of teachers out of work more than doubled to 1,800 over the summer.

The job fair, at the Armory on the Hudson in Upper Manhattan, is by invitation only and teachers must register in advance.

Education officials said the pool of teachers looking for permanent positions spiked after approximately 1,000 teachers lost their positions at the end of last school year.

The number of teachers without a full-time position fluctuates seasonally. It is common for the absent teacher reserve, or ATR, to swell over the summer and then go down after teachers find permanent positions in the fall, said Connie Pankratz, a spokeswoman for the Department of Education.

But the city is trying to reduce the annual ATR pool size and ultimately get rid of those teachers who are being paid for full-time work but are not actively looking for jobs, or can’t get hired. Last year there were just 800 excessed teachers on the city payroll, something both education and union officials said was the result of a new system of rotating teachers to different schools each week, giving them more exposure to schools that may want to hire them permanently.

The system also encouraged principals to use teachers in the reserve pool as substitutes, rather than hire substitute teachers with funds from their individual school budgets.

In an effort to shrink the pool even more, the Bloomberg administration and teachers’ union have been negotiating a buyout plan for some teachers without permanent positions. Last May schools chancellor Dennis Walcott announced a proposal.

Walcott did not give any specifics at that time, but said about 200 teachers had been in the pool for at least two years and that about 365 of them had never submitted a job application online or attended a recruitment fair. Education officials also said that nearly half of the teachers in the pool at the time had received a disciplinary action or unsatisfactory rating in the past five years.