The Immigration and Nationality Directorate took the decision to close the Sunbeam Nursery, which is managed by Bright Horizons Family Solutions, without consultation.
Six-hundred parents have signed a petition organised by the Public and Commercial Services Union, which they intend to present to immigration minister Liam Byrne.
Many are concerned that the costs of making new childcare arrangements could force them to give up their jobs.
The Home Office has not said what alternative childcare provision, if any, would be offered.
The lease on Quest House, where the nursery is situated, does not run out until 2009. But union spokesman Ragesh Khakhria said he had been told that the nursery would be closed by the end of December.
He said, 'The lease doesn't run out for some time. There's no reason to close the nursery and they could just have put the nursery in another building. There are 11 Immigration and Nationality Directorate buildings in the area.'
He added, 'The Cabinet Office Toolkit talks about how civil service departments should be provided with workplace nurseries. The Home Office is going in the opposite direction, because they're closing a workplace nursery. We're moving to a regional structure in the Directorate, so I think if a workplace nursery is in one place, people will start demanding it in others, and that's what they don't want.'
The Home Office has yet to announce the exact date of closure. Bright Horizons Family Solutions executive director Susan Hay said, 'We haven't had a date finalised, but there is still a significant amount of time left on the contract, so we'd hope that parents won't be left in a difficult position.'
A Home Office spokesman said, 'The Sunbeam Day Nursery is currently used by 63 parents out of a total Immigration and Nationality Directorate workforce of over 16,000.
'The decision to close the nursery was taken because the lease on the building in which it is located was due to be surrendered, and re-providing the facility elsewhere did not represent best value for money.
'Immigration and Nationality Directorate staff are located across the country and have a variety of needs. We therefore need to offer parents a range of options for childcare. A variety of provision is the best way to make equitable arrangements for all staff irrespective of grade or location. On balance, we felt that the funding required to sustain the nursery in Croydon would be better spent in ways that benefited a wider group of staff.'