Unlawful. According to the query invoice related information, buy food to open catering invoice illegal. It constitutes the crime of falsely opening general invoices. The crime of false general invoicing refers to the false opening of VAT invoices or false opening of invoices other than invoices used to fraudulently obtain export tax refunds and tax credits, and if the circumstances are serious, the penalty shall be fixed-term imprisonment of not more than two years, detention or control, and shall be punished with a fine.