Costco’s planned expansion of its Issaquah headquarters is one step closer to completion following the city of Issaquah’s approval of a land use permit.

The Issaquah-based wholesale retailer hasn’t been able to expand its corporate headquarters for more than 25 years, and for the last 15 years it hasn’t been able to add capacity to its campus in the Pickering Place development because of transportation limitations within its master plan. Costco has been leasing nearby office space and is looking to bring some 2,000 employees currently working off-site onto a new, expanded campus.

Costco is hoping to double the square footage of its office and support facilities. On top of providing room for current employees, it will be able to hold an additional 1,500 workers once the expansion is completed. About 600,000 square feet of new office space will be built as part of a new nine-story office building above a level of parking. A 10-story parking garage will be constructed as well, with the first level housing an exhibit space and lobby.

City of Issaquah communications coordinator Thomas Rush said Costco had grown its employment base by leasing vacant office space in Issaquah. Costco is the city’s largest employer and keeping the retailer headquartered in Issaquah was a top priority for the city’s economic development department, Rush said.

Issaquah and Costco signed a development agreement in 2014 giving Costco the right to add 1.5 million square feet of new office space in the area around their campus on the condition that the company paid traffic mitigation fees up front. As part of the development agreement, the city of Issaquah and Costco agreed to split costs for three transportation projects which were expected to cost $51.5 million. Costco’s share of the price tag was about $24.7 million.

Costco did not respond to a request for comment for this story.