The San Diego Unified School District Board of Education Tuesday night approved an agreement with unions regarding the use of labor on Proposition S projects, but less revenue is coming in from bond sales than expected.The Project Labor Agreement, approved on a 3-2 vote, describes the conditions under which workers will be employed by contractors for construction under the $2.1 billion bond measure, which was passed by voters last November.The agreement includes hiring preferences for workers who live within the school district's boundaries and sets standards for livable wages and benefits."We're really excited about the future and putting San Diegans to work," said Tom Lemmon of the San Diego Building and Construction Trades Council.Backers of the agreement believe it will save money, because it ensures projects will be finished on time and bans work stoppages.The agreement drew opposition from contractors who claim it effectively bars non-union construction firms from bidding on the jobs. Opponents also said requiring union contractors will drive costs beyond what the bond measure will bring in and, ultimately, fewer projects will be completed."It's going to cause more problems and cost more money for this district," said board member Katherine Nakamura, who along with John De Beck voted against the agreement.Nakamura also protested a provision that requires 35 percent of a project's employees to reside in ZIP codes identified as economically disadvantaged, which would limit opportunities for construction workers in the area she represents.Board President Shelia Jackson countered that the 35 percent figure is too low because 65 percent of the district's students qualify for free or reduced-price lunch, indicating poverty.At a special meeting earlier in the day, board members were told that less money was coming in from Proposition S bond sales than expected, so district officials might have to reshuffle plans for renovating schools.The district expects to get about $100 million from the sale of the bonds for the next academic year, about $20 million less than projected, said Stuart Markey, the executive director of the district's bond program.Markey expects $20 million to $25 million less in bond revenue in each of the following years.Interest rates and market conditions can affect revenues from bond sales. If the economy improves markedly, revenues could eventually match the initial projects, he said.