Unite members at Legal & General's flagship site in Kingswood, Surrey have voted in favour of industrial action to save over 1,500 jobs.
In an industrial ballot 67% of union members voted in favour of industrial action short of a strike, which can include working to rule or refusing to work overtime.
Ian Methven, Unite regional officer said: "Legal & General is a company which relies on staff going the extra mile, from working late to volunteering for overtime.
"Our members are dedicated and hardworking professionals, but today's result shows that a tipping point has been reached and their goodwill can no longer be taken for granted. Frankly, the cost to the company is incalculable."
The dispute follows L&G's decision to threaten 1,550 jobs by closing the Kingswood site in 2017, citing potential cost savings.
Unite has been campaigning since September to keep the site open.
In response, L&G has postponed the closure of Kingswood until 2018 and have offered some staff the option of relocation to sites across the country.
Methven added: "Unite is calling on Legal & General to work with us to explore all options that can keep Kingswood open. Closing the site will not only cost 1,550 people their jobs, it will devastate the surrounding community.
"We are grateful to the local businesses and politicians who are supporting our campaign to defend Kingswood and all the jobs that rely on it."
