The first minister of Wales would veto the so-called sterling zone if Scotland voted for independence in the September 2014 referendum.
Carwyn Jones said that he did not believe that the Scottish government's argument that a currency union would be in the best interests of a newly independent Scotland and the rest of the United Kingdom was credible.
"If we have a currency union, how does it work? You either have an independent central bank in which case independence takes you nowhere or you have a scenario where different governments have to agree to take actions at different times and that just leads to dithering," Jones told BBC Scotland.
"Where would we be for example in 2008 where there was a need to take decisions within hours to save certain banks? If we had different governments trying to agree on that you would end up with dithering. The idea of a currency union is nothing like as straightforward as it seems," he added.
His comments came on the back of speech at the University of Edinburgh in which he made a case for the union. That speech followed a Treasury response to the Silk Commission on the devolution of financial powers to Wales.
It announced that Welsh ministers would get tax-varying powers, full control of business rates and early access to borrowing powers.
Jones told the audience in Edinburgh that the agreement showed that further devolution for Scotland could be possible if it chose to stay within the UK.
"I am a Labour politician. I am a fluent Welsh speaker. I enjoy and cherish Wales' cultural distinctiveness. I am a fierce supporter of our national rugby team. In short, I feel very patriotic about my country. I want the very best for my country.
"And I would say to Labour voters, you can be a patriotic Scot and still want to stay in the UK - because that's what's best for your country. The referendum decision is entirely a matter for the Scottish people but its implications will be felt way beyond your borders.
"I ask you not to forget your friends in Wales and in the wider UK. A strong Scotland in a strong UK is a positive choice."
The SNP's economic vision for Scotland would follow the recommendations of Scotland's economic advisers, the Fiscal Commission Working Group.
One is that Scotland should establish a "sterling area sustainability agreement" that would be negotiated with Whitehall.