The number of workers retained at the passport office in Newport could be as few as 30, MPs have been told.
Sarah Rapson, of the Identity and Passport Service (IPS), told the Welsh Affairs Committee between 30 and 45 jobs would remain.
She confirmed to the committee at Westminster that it could be "as low as 30".
More than 250 jobs are expected to go if plans to close the existing office are approved.
Home Office minister Damian Green is also due to give evidence to the committee.
The meeting was called after Mr Green, the minister who is in charge of passports, announced at the beginning of October that consultation was to begin on the closure of the Newport office.
The decision sparked an angry response from unions, opposition politicians and staff, with hundreds taking to the streets of the south Wales city in protest.
Welsh Secretary Cheryl Gillan later announced up to 45 jobs would be safeguarded.
Giving evidence to the Welsh affairs committee, Ms Rapson said: "We are looking at a range of between 30 and 45."
When asked by the Newport East MP Jessica Morden if that meant the number of staff retained could be as few as 30, Ms Rapson said: "It may be as low as 30, yes."
The IPS has insisted that the changes are necessary to reduce the size of the organisation and ensure it is more efficient.
It said its analysis had found that closing the Newport office would result in "the greatest reduction of spare capacity at the lowest cost to the taxpayer".
But Labour Newport West MP Paul Flynn has described the proposal as "butchery".
The Welsh affairs committee, which is chaired by the Conservative MP for the neighbouring constituency of Monmouth, David Davies, will also hear evidence from the PCS union and Newport city council.