Is it permissible to complain about a colleague who monopolizes work and prevents others from doing it to government agencies such as tax authorities, or is that forbidden?

The Prophet, peace and blessings be upon him, said: "Leave people; Allah provides for some of them through others." So, if the person mentioned prevents people from working and trading in a certain field without a just cause, he is an oppressor and acts against the Sharia. It is permissible to sue him and contend with him until his harm and oppression cease. However, it is not permissible to cause an oppressor to be set upon him who would take from him what is not rightfully theirs.