Not illegal. Strictly speaking, customers need invoices for consumption, and businesses must issue invoices and not refuse to accept them, otherwise it is illegal. However, in reality, small shops have not collected from the tax bureau because they rarely ask for invoices. It's not illegal. If you really need an invoice, you can issue an invoice voucher and affix the official seal of the unit. The snack bar will invoice the tax department. Article 52 of the Law of People's Republic of China (PRC) on the Administration of Tax Collection, if the taxpayer or withholding agent fails to pay or underpays the tax due to the responsibility of the tax authorities, the tax authorities may require the taxpayer or withholding agent to pay back the tax within three years, but shall not impose a late fee.

Legal objectivity:

Article 19 of the Measures for the Administration of Invoices in People's Republic of China (PRC): When units and individuals sell goods, provide services and engage in other business activities and collect money from outside, the payee shall issue invoices to the payer; Under special circumstances, the payer will issue an invoice to the payee. Measures for the Administration of Invoices in People's Republic of China (PRC) Article 20 Units and individuals engaged in production and business activities shall ask the payee for invoices when purchasing commodities, receiving services and engaging in other business activities. When obtaining the invoice, you are not allowed to change the name and amount.