Withholding tax is a method of collecting income tax in advance from the recipient's income through the payer. It is commonly applied to salary income under section 149, and to sales of goods, services, and transportation under section 153. When opening a supplier account, details like NTN/CNIC number, company/individual status, and any applicable exemption certificates should be collected. Withholding taxpayers must file monthly and annual returns and undergo a yearly audit.