Barth denies the doctrine of Justification by Faith Alone

... in 1935 Karl Barth published a little book entitled Gospel and Law. In reversing the usual Protestant order of law and gospel Barth was indicating by the title itself his dissent from ordinary Protestant ways of thinking and speaking. Hans Küng helps us to see Barth's conflict with the Reformation clearly in his book on Barth and justification. Küng wrote, "It is to be presupposed that the justified man is truly just — inwardly in his heart. At this point Barth does side with Trent against the Reformation... Justification is not merely an externally pasted-on 'as if'. Man is not only called just but is just."¹ In the preface to Küng's book Barth acknowledge that Küng has presented Barth's position accurately and states that if Küng accurately has presented the Roman Catholic view, then they are agreed.

— W. Robert Godfrey, Westminster, Justification, and the Reformed Confessions. In David VanDrunen (ed.), The Pattern of Sound Doctrine: Systematic Theology at the Westminster Seminaries. Essays in honor of Robert B. Strimple (Phillipsburg, NJ, USA: P&R publishing, 2004), 132

[1] Hans Küng, Justification: The Doctrine of Karl Barth and a Catholic Reflection (New York: Westminster, 1964), 236

If indeed the doctrine of Justification by Faith Alone is the doctrine by which the church stands or falls (articulus stantis et cadentis ecclesiae), then Barth's doctrine of justification puts himself outside the pale of orthodox Christianity, nevermind the Reformed tradition.