Wales has warned it may shut its borders to people coming in from coronavirus hotspots such as Liverpool.
First Minister Mark Drakeford has confirmed he will write to Boris Johnson today to convince the Prime Minister to stop people crossing the border from high risk areas.
Liverpool has been placed under strict Tier 3 lockdown measures which come into effect on Wednesday.
Under the measures travel out of the area is advised against, but hasn't been banned or made illegal.
Speaking on BBC Wales Today on Monday evening, the First Minister said closing the Welsh border was "not the preferred option" but that the Prime Minister's guidance "simply will not do" - reports Wales Online.
He said: "North Wales Police cannot stop someone and turn them around simply because they're not following guidance.
"We need rules that prevent people from high incidence areas coming into Wales, to areas with low incidences of the virus."
Mr Drakeford said he would be writing to the Prime Minister showing the harm being done by those coming into areas of Wales with low infection rates, to give Mr Johnson "one final opportunity to do the right thing."
Mr Drakeford said: "We've got that evidence, we'll share it with the Prime Minister. I will set out the powers that we have, and if he doesn't act, we'll use them.
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"I want to give him one final opportunity to do the right thing. Because that would be fair to people in Wales and people across the border.
"The Prime Minister needs to act. He has the power, he has the authority, what he lacks is the willingness. He needs to find that."
