The opening of a specialist coronavirus testing lab in Newport has been delayed until next month.
It had been hoped the Lighthouse Lab, at Imperial Park, would be up and running in August.
The UK government has not explained the delay. Public Health Wales (PHW) said it was due to "ongoing recruitment" and laboratory "validation".
Lighthouse Labs are a network of specialist Covid labs managed by the UK government and run by private firms.
US diagnostics company Perkin Elmer is running the Newport lab and is recruiting 200 staff.
In July the Welsh Government said PHW would be working with the UK government "to get the lab up and running".
On Wednesday, Quentin Sandifer from Public Health Wales told a Senedd committee he had asked the UK government department of health about the delay.
"We have enquired and it's our understanding that there are a combination of factors, including still ongoing recruitment and matters to do with the validation of the laboratory before it can go live," he said.
Lighthouse Labs, where most Welsh samples are sent, have been beset with difficulties.
Big backlogs have meant many people have been unable to access tests close to home.
The UK government said equipment is in place at the lab and staff have been recruited.
A spokeswoman said: "In the last few months we have rapidly built the largest diagnostic testing capacity in British history, outstripping all major countries in Europe with more testing per head of population.
"We have new lighthouse laboratory capacity coming online, including in Newport, Newcastle, Bracknell and Charnwood, as we drive towards our testing capacity target of 500,000 a day by the end of October."
Newport West Labour Senedd member Jayne Bryant said: "When we're seeing an increase in demand for testing, the delay by the UK government to the promised Lighthouse Lab at Imperial Park in Newport is very disappointing and frustrating to say the least.
"The UK government needs to urgently resolve the issues with the Lighthouse Labs, which we're seeing across the UK, to ensure we have capacity in the system."