Up to two-thirds of the Charity Commission's staff might take part in a 48-hour walkout next week as part of national strike action by public servants angry about changes to their redundancy terms.
The Public and Commercial Services Union, which has about 60 per cent of the regulator's 500 staff as members, voted in favour of strike action last week.
The strike will take place on 8 and 9 March. Dates for further industrial action will be discussed this week, with PCS threatening weekly walkouts.
The union claims the changes to the civil service compensation scheme would mean staff would lose up to a third of their current redundancy entitlements.
Mark Serwotka, general secretary of the PCS, said: "With civil and public service jobs increasingly at risk, this is a cynical attempt to cut jobs on the cheap, which will ultimately damage the services we all rely on."
A spokeswoman for the commission said the regulator had contingency plans in place to manage any reduced staffing. "We will work hard to minimise the disruption caused to our customers," she said.