The Welsh and UK governments are on course for a major confrontation with the First Minister accusing the Prime Minister of planning an ''assault on devolution.''
During the election campaign, the Conservative Party promised to ensure an M4 relief road around Newport will be built, a project rejected by the Labour Welsh Government.
But Mark Drakeford told Monday night's Sharp End programme that there is no way back for the scheme while he is First Minister and that it would be wrong for the Prime Minister to try and force a u-turn.
Asked if there was any way back for the M4 relief road, Mark Drakeford said: ''Not while I'm First Minister because I've made my decision and it is an entirely devolved decision."
''The Prime Minister has no say in the M4 relief road whatsoever.'' Drakeford insisted that even if the UK Government paid for the relief road, he still would not go ahead with the plans.
''It is not for Mr Johnson to pay,'' he said.
''It is not the way the system works. Then you're talking about very big changes indeed and a Prime Minister that would launching an assault on devolution because the way devolution works is the money comes to the Welsh Government and it is then for the National Assembly of Wales to decide how the money is spent, not for a Prime Minister in London.''
It seems a larger and reinvigorated group of Welsh MPs is up for the fight. Also speaking on Sharp End, three of the new Welsh MPs promised to challenge and hold the Labour administration to account.
Sarah Atherton, Virginia Crosbie and Fay Jones made history after becoming the first female Welsh Conservative MPs.
''What we've had is a Labour lock and as Conservatives we're challenging that and scrutinising that.'' Atherton said.
Crosbie added,''By calling them to account. I think they've got away with it for too long and people have shown us that by the way they voted.''
''Particularly in the rural areas like Brecon and Radnorshire,'' Jones said.
''A lot of people think that there isn't life beyond the Heads of the Valley's road. That's certainly an attitude that a lot of my constituents feel. They feel that Welsh Labour just isn't interested in them so we need to challenge that.
''We have to put pressure on the Welsh Government...we have an awful lot of influence and we can use that to put pressure on them to act.''
Speaking to ITV News, newly appointed Welsh Secretary Simon Hart said UK Government would not bypass Drakeford in making a decision on the relief road but would ''try to find ways to make it possible.''
''There's not a soul who use that road who doesn't believe that there isn't a problem.'' Simon Hart said.
''We will play our part in trying to resolve it, I hope Mark Drakeford will do the same.
''If the UK Government provide infrastructure funding, for example, or creates a project which improves people's lives then I think it's difficult for Welsh Government to say, 'not only do we disagree with UK Government but we disagree with Welsh businesses and Welsh voters.'
''I think that's a hard position for them to be in.''