By Mary Wisniewski
CHICAGO (Reuters) - A bargaining team for the Chicago teachers' union on Monday unanimously rejected a four-year contract offer from the financially troubled city, raising the possibility of a strike and possibly causing a new embarrassment for Mayor Rahm Emanuel, the Chicago Sun-Times reported, citing a source.
The rejection means the union and Chicago Board of Education will enter a final stage of talks that starts a 105-day clock ticking toward a strike, the paper said.
The union had said it had received "a serious offer" from the Chicago Board of Education after over a year of negotiations.
According to local media reports, the offer asked teachers to pay more for retirement, but also offers moderate pay raises. These numbers could not immediately be confirmed.
Union leaders planned a news conference for later on Monday.
Teachers in the country's third-largest school system voted overwhelmingly in December to authorize a strike, which would be their second since 2012. The vote allowed a strike to proceed if union leaders decide it is necessary.
The potential for a strike, plus a decision last week to delay an $875 million bond sale, has increased the political strain on Emanuel, a Democrat and former chief of staff to President Barack Obama.
Meanwhile, a proposal pushed by Illinois' Republican lawmakers for a state takeover and potential bankruptcy filing for the school system made some investors nervous.
The district, which serves about 400,000 students at more than 600 schools, is struggling with a structural budget deficit of at least $1 billion and cash-flow that is dependent on borrowing.
Emanuel has blamed state government, which gives Chicago schools 15 percent of state education funding, though it accounts for 20 percent of the state's public school students.
A recent violent crime wave and the November release of a video showing the fatal shooting of a black teen by a white police officer has hurt Emanuel's standing among voters. A Chicago Tribune poll released on Monday showed Emanuel's approval rating at a record low of 27 percent.
(Reporting by Mary Wisniewski, editing by G Crosse)