Another legal opponent of Turtle Bay Resort’s expansion plan has agreed to settle its lawsuit, becoming the second of three plaintiffs to reach an accord.

The resort announced the latest agreement with the Sierra Club Tuesday, a week after reaching a deal with community organization Keep the North Shore Country.

The two entities, along with hotel worker’s union Unite Here Local 5, challenged the validity of a supplemental environmental impact statement supporting the addition of two hotels with a combined 625 rooms and 100 homes on about 150 acres fronting the ocean on opposing sides of the existing 443-room Turtle Bay hotel.

If the resort can work something out with Local 5, it said it can complete a historic arrangement to protect much of its North Shore property from development in perpetuity. Discussions with the union are ongoing, the resort said.

Turtle Bay agreed last year to sell the state a conservation easement covering more than 666 acres that includes much undeveloped land and two existing golf courses for $48.5 million. The city and The Trust for Public Land chipped in $5 million and $3.5 million, respectively.

The easement will effectively eliminate 650 homes from the resort’s expansion plan, including 225 fronting Kawela Bay.

Terms of the Sierra Club settlement weren’t disclosed, though part of it allows the environmental organization to add 32 acres of resort property fronting the ocean west of Kahuku Point to the preservation area if money for the addition can be raised. A price to protect the 32 acres was not disclosed.