Belfast is reporting a surge in demand for Covid-19 tests by health care workers, leading to claims that some have been unable to secure an urgent appointment.
One health care worker said she tried dozens of times to phone the number given to make an appointment - but the call dropped automatically every time.
Belfast Health and Social Care Trust said there was a surge in calls on Monday and that some workers, and family members, waited for around 30 minutes to get through to make an appointment.
A relative of one health care worker said she went to work on Monday showing symptoms of a cold. She was told to go home and to get a test.
But when she tried to call to make an appointment, she was unable to do so that day. When the health worker managed to get through the following morning, the operator spent 15 minutes taking her personal details.
"She was so angry because this was a number for NHS staff," the relative said.
"It rings, says we are busy, then cuts off. You would think six months down the line it should be a smooth operation. If frontline staff are having difficulties, what is it like for the rest of the public?"
And on Twitter, West Belfast Sinn Fein MLA Pat Sheehan said he was told to go to Stranraer in Scotland for a test for his four-year-old daughter.
He described the booking system for Covid-19 tests as a "shambles".
"We've been at this for six months now, you would expect any difficulties there were would've been ironed out," Mr Sheehan told BBC News NI.
"My case isn't an isolated case, there seems to be a lot of people facing the same difficulties."
Belfast Trust said that staff who wish to enquire about testing must first contact the Occupational Health department.
"If a member of staff is advised they need a test they are given the number for the test booking line which is answered by Belfast Trust staff," it said.
"Each telephone call can take time to complete so all relevant and correct information can be captured accurately. A typical call may require logging the details of multiple family members and can take up to 20 minutes.
"This telephone line has experienced a surge in demand since Monday, September 7 and callers have told us that they have been waiting for around 30 minutes to get through.
"We apologise to any staff who have had to wait for long periods of time and we would ask them to please bear with us while we work through this extremely busy period."
The Department of Health said it is the responsibility of each of the trusts to organise testing for staff.
Health Minister Robin Swann said yesterday he has contacted his Westminster counterpart, Matt Hancock, over Covid-19 testing.
Mr Swann said he is seeking action on a number of points, including the UK-wide online booking system that has been offering some people in Northern Ireland tests in Great Britain.
"To be clear, no one in Northern Ireland is expected to travel outside the jurisdiction for a test," he said.
"These slots have been offered by the online system because it has not on occasions recognised local requirements. The same problem has been reported in Scotland.
"I have also emphasised the need to urgently build capacity for the National testing programme."
Sinn Fein MLA Colm Gildernew has called on Mr Swann to ensure that people can access testing and that enough home kits are made available amid growing concerns over shortages.
"Given the sharp rise in cases, this is deeply concerning. Testing capacity needs to be ramped up rather than delayed," he said.