taxes

Q: In our country is it necessary to pay income tax. If one does not pay the tax from his salary or money, then will that money become haraam?

Q: An employee works for a company and his stipulation is not set at the beginning. He is paid an amount less than the market rate for such a job. Secondly, the employer places the entire burden of taxes on the employee, whereas the employer is required by law to pay 7.65%. The employee works because he cannot find another job currently, is this Zulm on the part of the employer?

Is it permissible for him to take on clients on the side and complete work in the office and keep the compensation for that? What if he pays for his own supplies such as papers, pens, etc?