CHICAGO – Angry that one promised raise disappeared and that they’re being asked to work longer days without what they consider to be an adequate pay increase, Chicago teachers are considering authorizing their first strike in a quarter-century.

In a signal of their mounting anger, teachers are voting this week — before a summer of negotiations and a recommendation from an independent fact-finder — on a strike that wouldn’t happen until the next school year starts. If they do authorize a strike, teachers in the nation’s third-largest school district would be leaving the final decision in the hands of union leaders.

“This is a reflection of the treatment we as teachers have been subjected to this year … that the posturing of the board of education has created such misery and suffering and discontent that we needed to send a message,” said David Rose, a teacher at Roberto Clemente Community Academy.

The frustration largely revolves around Mayor Rahm Emanuel, who rescinded a 4 percent raise last year and then began pushing for a longer school day. Teachers say the mayor — and now the district — have not offered them enough to make up for the added time.

Chicago Public Schools has proposed a five-year deal that guarantees teachers a 2 percent pay raise in the first year and lengthens the school day by 10 percent. The union wants a two-year deal that reduces class size and calls for teachers to receive a 24 percent pay raise in the first year and a 5 percent pay raise in the second year.

Under a new Illinois law, at least 75 percent of the district’s 25,500 teachers would have to vote in favor of a strike authorization. The union is expected to release results next week.

For his part, Emanuel has said he thinks teachers do deserve a raise.

He also said he believes the two sides can find “common ground” and urged teachers to wait for the fact-finder’s report, which is due in mid-July.