Police will struggle to enforce new regulations on wearing face coverings on public transport, it has been warned.
Face coverings become mandatory here from today.
But many question how - and even if - people will be made to comply.
The PSNI last night indicated that it will rely on "other bodies" to help enforce the rules.
The regulations apply to bus, train and ferry services. The face coverings will also be required at stations.
Exemptions include those who cannot wear face coverings for medical reasons, children under 13, outdoor ferry areas and school transport.
Face coverings include any material that covers a person's nose and mouth; it does not have to be a surgical mask.
Assistant Chief Constable Mark McEwan said: We continue to work very closely with our colleagues in the transport industry.
"Police are designated to enforce these regulations. We continue discussions with the Department of Justice as to which other bodies will also be designated to enforce the regulations."
Mark Lindsay, chairman of the Police Federation for Northern Ireland, said there are "obviously" issues around enforcement of wearing face coverings.
He said that, in the first instance, it should be a matter for Translink to inform passengers what is expected of them and why.
"Police officers are already under considerable pressure keeping abreast with all the changes to regulations and lockdown restrictions," he added.
"It is unrealistic to expect the police to be able to deal with every single suspected breach of regulations, which tend to change on a daily basis."
TUV MLA Jim Allister added that the rule is a "very invasive infringement of rights", as are the other Covid-19 regulations, but he does understand why it has been brought in.
Mr Allister felt enforceability will be a "difficult issue".
Ian Campbell, Translink's director of service operations, said that fixed penalty notices will be used as a last resort.
"The majority of situations can be dealt with by our staff," said Mr Campbell. "We have existing protocols with the police so it's only really if it gets out of hand and it becomes an anti-social behaviour issue before we would engage with the police.
"If the customer determines that they don't need to wear a face mask, there's no identification needed. If the customer identifies a reason why they can't wear one then that's fine and they can travel without one."