PTSB is to broaden a voluntary redundancy scheme that was launched in October for senior managers.
It will now be open to all staff in the bank.
In a message to employees, PTSB said that since launching the scheme, it has received a number of informal expressions of interest from staff at all levels requesting that the scheme be extended to the wider bank.
"Reflecting on this interest and the bank's strategic direction, we have decided to broaden the scope of the scheme to invite applications from colleagues at all levels across the bank," the memo to staff stated.
PTSB has not said how many redundancies it is seeking.
"Following a period of transformational growth, the bank is now undertaking a number of important strategic business transformation change initiatives to enable its strategy and improve organisational effectiveness and efficiency," PTSB said in a statement.
"These initiatives will ensure that the bank's business model is both robust and sustainable into the future," it added.
The Financial Services Union (FSU) described the announcement three weeks before Christmas as insensitive and a devastating blow for consumers and staff.
"There has been no discussion with the FSU around this announcement and no signal to the staff that a redundancy programme was imminent," said John O’Connell, General Secretary of the FSU.
"To announce this a few short weeks before Christmas is upsetting for staff and shows poor judgement from the bank," Mr O'Connell said.
The FSU said it is calling on the Central Bank to intervene and ensure PTSB has appropriate staffing levels to meet the provision of access to cash and banking services around the country.
