Complaining is one of those bad things that are not accompanied by a "Thou Shall Not" commandment.
We know that complaining is a bad thing to do because of what happened to people in the Bible who complained.
Complaining Against MosesWhen the Israelites entered the Wilderness of Sin, they did not have food to eat and they complained against Moses and Aaron and said, "It would have been better if God had killed us in Egypt when we sat beside pots of meat and ate bread till we were full because you have brought us to this wilderness to kill us with hunger". (Exodus 16:1-3)
The next verse tells us that God told Moses that He would rain bread from heaven for them to eat. (Exodus 16:4)
Moses and Aaron did not have to tell God the complaints the Israelites had made because He had heard them.
Moses then told the Israelites, "God hears your complaints against Him. For who are we that you should complain against us? Your complaints are not against us but against God." (Exodus 16:8)
This teaches that you should not complain against the spiritual leaders that God has chosen to lead you because the Israelites did not find themselves in the Wilderness of Sin because of Moses, they found themselves there because Moses was following God's leading.
Therefore by complaining against Moses' leading, they were complaining against God.
So do not complain against your spiritual leaders. If they have done something you do not understand, pray to God about it rather than complain about it.