The Brexit transition period should be extended as the UK tackles the coronavirus outbreak, the Welsh Government has said.
A letter from Mark Drakeford to the prime minister says not doing so could cause a further "economic shock".
The UK plans to negotiate a deal with the European Union by the end of the transition, in December.
Conservative assembly member Andrew RT Davies said Mr Drakeford's intervention was "bizarre".
In his letter the first minister said it seemed "simply implausible to continue the negotiations to the timeframe originally envisaged, under these circumstances".
Until the end of December the UK is adhering to the rules of the EU, despite officially having left the bloc in January.
NEW: @fmwales has written to @BorisJohnson calling for a pause in the UK-EU post-Brexit talks.— James Williams (@jamswilliams85) March 24, 2020
Mark Drakeford says an extension to the transition period beyond the end of 2020 is needed so that governments can devote their “full attention” to fighting coronavirus. pic.twitter.com/j0gFZRRgH8
In response to a question last week from Labour MP Stephen Kinnock about whether government would request an extension to the transition period, Foreign Secretary Dominic Raab said negotiations could proceed.
"We are confident that we can get this done, and I do not think that delaying Brexit negotiations would give anyone on either side of the channel the certainty they need," Mr Raab said at the time.
Mr Drakeford said the governor of the Bank of England "has painted a very sober picture of the economic impact of Covid 19 in the period ahead".
"Now is clearly not the time to contemplate adding the kind of economic shock that would accompany any change in trading relationships with the EU at the end of 2020, on top of the full-blown economic challenge no unfolding," the first minister wrote.
"I urge you, therefore, to seek a pause in negotiations with the EU and to seek an extension to the transition period," he said, saying the negotiations could be resumed in "more normal and viable circumstances".
Andrew RT Davies, Conservative AM for South Wales Central, said: "Every single sinew of Welsh Labour Government resource, time and energy should be tackling the Covid-19 crisis and nothing else.
"Pushing the Prime Minister on Brexit at this juncture is both bizarre and inappropriate, particularly given he has a number of more pressing matters to deal with such as the health of the nation."