In Numbers 12 comes an attack on Moses' authority from those closest to him, his siblings Miriam and What is the true nature of their complaint and their attitude toward God-given authority?
They both got jealous with Moses. The fact that God communicated to them also got to their heads. Looks like they justified to themselves by looking at the fact that Moses had married a Cushite woman.
Here are the verses:
While they were at Hazeroth, Miriam and Aaron spoke against Moses because of the Cushite woman whom he had married (for he had indeed married a Cushite woman); 2 and they said, “Has the LORD spoken only through Moses? Has he not spoken through us also?” And the LORD heard it. 3 Now the man Moses was very humble, more so than anyone else on the face of the earth
The Holy Bible: New Revised Standard Version, Catholic Edition (Nu 12:1–3). (1993). National Council of Churches of Christ.