The Nashville Sports Authority's board of directors voted Thursday to hire a joint venture of two construction firm to build the city's new Major League Soccer stadium after a lucrative contract had been held up by protest from another bidder.

At the same meeting, a group of union members asked that the city use "high-road" subcontractors for the stadium construction to ensure worker safety, health insurance and other work standards.

The sports authority approved an agreement that expresses an intent to award the joint firm of Mortenson | Messer Construction Co. a construction manager contract valued at $167.5 million

The agreement is still contingent on successful negotiations between the city and the firm.

Nashville's Metro Council this month voted to finalize a $275 million stadium project at the city's fairgrounds.

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The joint venture — a combination of Minneapolis-based Mortenson and Nashville-based Messer Construction Co. — in August received the highest score among four finalists for the contract according to a rubric as part of the city's bidding process.

But another finalist for the coveted construction contract, Barton Malow Co., had protested Metro's decision, prompting the sports authority to defer engaging Mortenson | Messer Construction Co. last month.

Michelle Hernandez-Lane, the city's purchasing agent, upheld the procurement decision at an Aug. 29 meeting. The firm had seven days to appeal, but chose not to. A third company, Skanska | AECOM Hunt, had contemplated appealing, but did not follow though

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Nashville Sports Authority Director Monica Fawknotson said the plan is to bring a final contract back to the board after all terms are completed.

"It needs to be thorough and we need to make sure that the parties are in agreement," she said of further negotiations. "But we need to do that in time-frame that makes sense, understanding that this is a time-sensitive project."

She said Metro plans to meet with representatives of Mortenson | Messer Construction Co. on Sept. 25.

Unions want CBA requirement to extend to stadium

The plan is for construction on the stadium to begin next year after the opening of a new expo center. It will be the new home of flea markets and other current fairgrounds events that take place at current facilities that will be torn down. The stadium is to open in 2021.

As the board discussed the contract, members of the union-aligned the group Stand Up Nashville held signs from the crowd urging Metro to hire only stadium construction subcontractors considered "high-road."

As part of a community benefits agreement ,or CBA, reached between the team owners and Stand up Nashville, high-road contracts are required for the construction of a 10-acre mixed-use private development next to the stadium. But it does not apply to the stadium itself, which will be built by Metro.

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They said high-road contractors, which are unionized firms, would keep the project free from wage theft, reliance on low-wage temp services, and avoidable workplace injuries.

"Our work now includes demanding the same standards that were agreed up on the private side of the development be applied to the public side as well," reads a letter from Stand Up Nashville that was delivered to the board reads.

"After all, we can't let the stadium undermine our strong CBA."

Reach Joey Garrison at 615-259-8236, jgarrison@tennessean.com and on Twitter @joeygarrison.