Staff at Companies House in Cardiff have been told to expect 11% cuts this financial year.
The UK government agency for registering businesses employs 1,100 people.
More details will be given to public servants during meetings on Thursday but Companies House says the cuts are necessary as part of £836m savings.
Union officials say the news is alarming but they hope any redundancies will be voluntary.
Mike Crimmins, the PCS branch chair at Companies House, said all the staff were going to be briefed by the chief executive on Thursday morning.
As well as the headquarters in Cardiff, around 200 staff also work at offices in Nantgarw, Rhondda Cynon Taf, while there are also offices in Edinburgh and London.
He said he hoped there would be a properly funded voluntary redundancy scheme and that the union had been reassured attempts will be made to avoid compulsory redundancies.
Companies House forms part of the department of Business, Innovation and Skills. It has got to find savings of £836m this financial year, or 3.9% of its total budget.
It is one of the first departments to be targeted as the new UK coalition government attempts to reduce the £156bn deficit as soon as possible.
A statement from Companies House said: "Companies House, together with all other parts of the Department for Business, Innovation and Skills, is required to find 11% this year.
"Matters have moved very quickly over the last few weeks and days, and directors here have been working hard to put in place effective plans and arrangements to make the cuts while still continuing to provide excellent services to our customers.
"Some of the early details will be announced to staff simultaneously throughout our UK offices, the HQ of which is in Cardiff."
The department insisted it was in dialogue with trades union representatives and would be working with them to provide information over the next few months.
The statement added: "It is a fundamental part of government thinking that effective customer facing services should continue to focus their efforts on frontline provision and Companies House has an excellent reputation in this regard, gained over many years and in sometimes difficult circumstances.
"Our role in government is crucial to supporting British business development and, as such, Companies House will continue to play its part in creating the right environment for economic recovery."
Plaid Cymru AM Chris Franks said central government's cuts could set the economy of Wales back for generations.
He has tabled an emergency assembly question regarding the situation but states the Welsh government had no say in the matter.
The South Wales Central AM said: "This is a difficult time for the staff at Companies House and their families. It is an example of the cuts from the government in London.
"Many more people work for the public sector in Wales so we will be hit harder.
"I hope the people in Companies House will be able to get the help they need to get new skills if faced with redundancy."
The Conservative-Lib Dem coalition government has already outlined plans for £6.2bn of cuts this financial year.