The First Minister has written a letter to the prime minister urging him, again, to introduce measures to ban people living in England's Covid hotspots from travelling to Wales.
Mark Drakeford attended a Cobra meeting chaired by Boris Johnson on Monday where he described the proposals put forward as "inadequate". Mr Drakeford said he expressed "deep disappointment" during that meeting.
He also told ITV News if an announcement wasn't made on the matter, the Welsh Government would look to use its own powers.
In the letter, he said said voluntary guidance on travel has proved "ineffective" and "firmer action is urgently required to keep the virus under control".
With the majority of Wales under local lockdown, the First Minister said the lack of action on the matter was "undermining the efforts in Wales".
Our efforts are being undermined by travellers from high-prevalence areas in other parts of the UK travelling to Wales.
He described the issue as UK-wide and said he was urging the First Minister of Scotland and the First Minister and deputy First Minister of Northern Ireland asking them to regulate travel in a similar way.
He said it would be "better" if all four nations were to act together, but in the absence of that, he will "act to keep Wales safe."
Using the tiered system that the UK Government announced for England on Monday, people living in tier 2 areas are advised not to travel outside of the area unless the journey is necessary.
In tier 3 they are advised the same, and also not to stay overnight in another part of the UK.
Asked about the possibility of the Welsh Government imposing travel restrictions, the prime minister's official spokesperson said, "There are no physical borders between Wales and England ... but we have delivered a very clear message that people in very high risk areas in England should not travel out of their areas."
Plaid Cymru called on the First Minister to act and called for "leadership not letters".
The party's leader Adam Price said, "Rather than writing another unanswered letter or waiting for a four-nation COBRA, why not act independently now in the interests of the people of Wales? If you need extra parliamentary time this week, First Minister, to get this legislation through, then we as an opposition party will support you. Can we really afford to wait another day, let alone another week?"
The Welsh Government also announced on Tuesday it was actively considering introducing a circuit break lockdown - of about two or three weeks - to control the spread of Covid-19. Mr Drakeford asked for another Cobra meeting to discuss those measures following the news the UK Government "ignored" scientists' advice on the matter.
The rest of the letter in full:
"From a public health response perspective, it is more straightforward to identify chains of transmission and manage outbreaks if there is less movement of people across administrative boundaries."
"It would be better if all four nations were to act in concert, but in the absence of an agreed way forward, I will act to keep Wales safe.
"I have been clear throughout that this is not a matter of the border between Wales and England. This is a matter of preventing the circulation of the virus from areas of high prevalence to low-prevalence wherever they may be.
"If you fail to introduce the sort of measures we have already introduced in Wales, it will make this an issue which will undermine rather than support the successful operation of the border region.
"On a related matter, you also outlined at COBR(M) the three-tier model you intend to use to inform decision-making to limit the spread of coronavirus in England.
"In his remarks, the Chief Medical Officer for England was clear the baseline measures in tier three will not be sufficient to bring the R number below 1. At the same time, the Chief Scientific Adviser, yesterday said that a circuit breaker period would have that effect.
"That advice reflected the considerable work on circuit-breaker measures carried out by SAGE, which can be effective in the circumstances we are now seeing in various parts ofthe UK.
"As I suggested yesterday, we should discuss collectively what circuit-breaker options might best serve to bring the virus – and the R number – under control across the UK. I would therefore request again that you urgently convene a further meeting of COBR(M) specifically to discuss circuit-breaker measures.