Video report by Rob Shelley
The ban on people visiting Wales from other areas of the UK with high levels of coronavirus has come into force.
It comes as tensions rise between the Welsh and UK governments, with the First Minister previously saying the pandemic has "thrown a spotlight" on their "unsatisfactory" relationship.
Criticism of the First Minister has mounted, with claims the travel ban move is "anti-English" and "unconstitutional", and that it will be impossible for police to enforce.
But Mark Drakeford had said the Prime Minister's refusal to agree to implement travel restrictions showed the Conservative Party's "tin ear" to Wales.
He announced the travel ban on Wednesday, after repeated calls on Boris Johnson to enforce the restriction were ignored.
In Friday's press conference, the First Minister did reveal that he had finally received letter of response from Boris Johnson and he had been "reassured" by its content.
Speaking at the Welsh Labour Together online event on Thursday, Mr Drakeford said: "It's thrown a spotlight onto our relationship with the UK Government, which as I've said many times, have not been what they need to be.
"There has been no regular, reliable rhythm, and when we have had it, it has not always been satisfactory.
However on Friday, Mark Drakeford confirmed that he had received a letter from Boris Johnson the previous day.
In the letter, the Prime Minister outlined why UK Government had chosen to only issue guidance against people leaving an area in England where coronavirus transmission is high - rather than enshrine it in law.
"Effective enforcement would be incredibly difficult and resource-intensive", he said.
Mr Johnson goes on to offer his "ongoing commitment to collaboration and alignment in decisions and approach across the UK."
Mr Drakeford said he found the tone of the letter "reasonable" and was reassured by Mr Johnson's reaffirmation to work together towards a common goal.
How will the ban be enforced?
The First Minister has said police will use technologies including number plate recognition to catch rule-breakers, but there are concerns this will put added pressure on services.
Mark Drakeford said officers will be able to apply practiced techniques developed earlier in the year, when people could not travel further than five miles in Wales.
But the Police Federation for England and Wales' Welsh lead said the varying rules between Welsh and English local authority areas will make the ban "unenforceable".
In a statement on behalf of the four Welsh police forces, Temporary Assistant Chief Constable Nigel Harrison of North Wales Policen said they are not at a time where officers will "robustly enforce the regulations where there are blatant breaches."
"We will not allow the selfish minority to risk the health of the vast majority who have sacrificed so much over the last few months."
"We intend to focus our activity on areas and behaviours that pose the greatest risk to our communities and we will be proactive in targeting those that are not sticking to the gathering rules, whether that be indoors or outdoors."
Will people be fined for breaking the rules?
The Welsh Government confirmed that fines for breaking the travel rule would be the same as those issued for breaching other coronavirus regulations.
This means a fixed penalty notice of £60 would be issued for a first offence, doubling for each repeated offence up to a maximum of £1,920. If taken to court over the matter, an even larger fine can be imposed.
Who is not allowed to travel into Wales?
Those living in tier two or tier three areas of England, the central belt of Scotland and the whole of Northern Ireland cannot enter Wales under the new rule. However people living in these areas would still be allowed to travel into Wales for work and for another reasonable excuse - similar to the excuses that apply to local lockdowns in Wales.
The regulations also work the other way - no one living in Wales should leave the country to go to any of the high-risk areas described above. Those living in local lockdown areas in Wales are already prohibited from leaving their local area anyway.