The Irish Blood Transfusion Service has said it needs more men to attend clinics to fill gaps in the blood supply.
This follows a decision last Monday to stop taking donations from certain women who have donated in the past due to issues with anaemia.
As of today the service has 2,400 units, which is about 300 fewer than normal.
It needs to increase attendances this week by 15%, which means getting around 600 donors attending clinics.
The IBTS said donations had decreased by around 12% in the past week.
Hospitals have been asked to conserve supplies and the IBTS has restricted access to O negative and A negative supplies.
Requests for these blood supplies are being referred to the IBTS specialist medical officer on call.
The service said that early indications are that more men are coming forward since the appeal a week ago but more are required.
It plans to arrange extra Sunday clinics over the coming weeks to boost supplies.
The IBTS expects to be back accepting both male and female donors by Monday 30 November.
It is reintroducing the haemoglobin check at clinics, while also continuing to take full blood counts from all donors attending.
Recently, the IBTS found that its haemoglobin test, introduced in July 2014, was failing to pick up iron deficiency in mostly female donors.
The issue has had no impact on the safety of blood received by patients.