What is the ruling of Islamic law on concealing some clients for the purpose of reducing taxes, based on the employer's order?

The ruling on tax evasion and aiding it depends on the type of tax: If the tax is lawful, it is not permissible to evade it or circumvent it, nor to assist anyone who does so, as Allah Almighty says: "And do not cooperate in sin and aggression." However, if the tax is unlawful, there is no objection to circumventing it and assisting the business owner in that, as a means of removing injustice and supporting the oppressed.