HMRC workers who are members of the Public and Commercial Services Union (PCS) are threatening to strike over a new employee sickness policy.
The action comes after a year of blunders at the Revenue, sparking several complaints the department cannot cope with its workload due to staff shortages.
In a ballot of over 50,000 PCS members, 59% voted to support a strike against an employee sickness policy.
Almost all members taking part in the ballot voted in favour of industrial action short of a strike.
PCS revenue and customs group secretary Peter Lockhart says: "This was a very good response to a ballot and, coupled with the clear vote in favour of action, it shows how strongly our members feel.
"We hope senior managers will now agree that trying to impose draconian new policies on their workforce is not the way forward, and we hope they will come back to the table with a willingness to resolve this dispute."
Two global vehicles
'Further plug advice gap'
Must appoint separate CEOs and boards
Advisers do come out well
Will report to Mark Till