Yale and union negotiators returned to the bargaining table Thursday, following a monthlong recess and increases in public hostilities on both sides.

At the negotiations, union leaders presented their plans for labor-management cooperation and best practices. Union officials also expressed concern about the climate toward unions on campus. The two sides have yet to reach agreements on economic issues including wages and benefits, as well as on issues of job growth, training and classification.

Yesterday’s meeting began the seventh month of off-and-on again negotiations between the two sides, and came amid a major change in tone between the two sides. Negotiations began in February with hopes of settling peacefully, but quickly deteriorated in pace and optimism during the summer.

Though the two sides have scheduled 10 more days of negotiations over the next three weeks, union leaders expressed frustration with the talks.

“We still are hopeful and optimistic that we can make all of this work, but it does require some significant changes on the part of the University and the climate that’s sort of been established on campus over the last few weeks,” Local 34 President Laura Smith said.

Yale spokeswoman Helaine Klasky declined to comment on specific negotiation issues.

“We see no reason that these negotiations can’t be concluded soon and that we get the best contract for all our employees,” Klasky said.

The contracts with locals 34 and 35 expired in January, and have been extended on a month-by-month basis since then. Workers have not received annual raises because new contracts have not been settled, and whether they receive retroactive increases has not been settled. The two unions represent nearly 4,000 clerical, technical, service, dining hall and maintenance workers.

In the weeks since the last negotiations, in early August, both sides have stepped up their public disagreements. In late August, Yale President Richard Levin wrote a letter to faculty, staff and students, in which he blamed delays in negotiations on union leaders, and said they had a broader agenda than settling contracts for their workers.

The following week, union members voted overwhelming to authorize leaders to call job actions, including strikes. The unions have been planning a day of civil disobedience Sept. 25, with plans to block traffic on a street near campus, and union leaders are considering a three-day walkout in October. Graduate Employees and Students Organization, the group trying to form a teaching assistant union, has also said it would hold a teaching strike if the unions hold a walkout, and hospital workers at Yale-New Haven Hospital also voted to authorize their own leaders to call a strike.

Smith said union leaders were disappointed that the University had not yet offered counterproposals to their initial economic offers, despite movement from the union to alter their proposal.

In early June, the University offered initial across-the-board annual wage increases of 3 percent for Local 35 and 4 percent for Local 34.

The unions initially proposed 7 percent annual increases for Local 35 and 10 percent for Local 34, but reduced the figures in their counterproposals, seeking 6.5 percent increases after the first two years of contracts for Local 35 and 9.5 percent annual raises after the first two years for Local 35.

The two sides have also disagreed on the length of the contract. Union leaders have asked for four-year contracts, while the University has proposed a six-year agreement.

Smith said union leaders also discussed their concerns about eight union members who had been arrested while distributing leaflets at Yale-New Haven Hospital in the last two weeks. The workers were arrested by hospital police and charged with criminal trespass. Four of them, who were arrested last week, will appear in court this morning.

University leaders said they had no part in the arrests because the University does not control the hospital. At the negotiations, union leaders said Levin should intervene to ensure workers are not arrested.