Is it illegal to refuse cash in school cafeterias?

It is illegal to refuse cash in school cafeterias.

According to Article 3 of the "Regulations of the People's Republic of China on the Administration of RMB":

The legal currency of the People's Republic of China is the RMB. All public and private debts within the territory of the People's Republic of China and the People's Republic of China shall be paid in RMB, and no unit or individual may refuse to accept it.

According to Article 6 of the "Regulations of the People's Republic of China on the Administration of RMB":

All units and individuals should protect the RMB. It is prohibited to damage the RMB and hinder the circulation of the RMB. Extended information

Announcement issued by the People's Bank of China in 2018:

In order to maintain the order of RMB circulation, protect the legitimate rights and interests of consumers, and regulate the tourism, catering, retail, transportation and other industries and Cash receipts and payments in administrative undertakings, public services and other fields are governed by the Law of the People's Republic of China on the People's Bank of China, the Law of the People's Republic of China on the Protection of Consumer Rights and Interests, and the Law of the People's Republic of China on the Protection of Consumer Rights and Interests. **Regulations on the Administration of Renminbi of the People's Republic of China", the relevant matters are hereby announced as follows:

1. The legal currency of the People's Republic of China is the RMB, including banknotes and coins (hereinafter collectively referred to as cash). No unit or individual may refuse to accept cash through formal clauses, notices, statements, notices, etc., except when non-cash payment tools are required by law.

2. On the premise of accepting cash payment, encourage the use of safe and legal non-cash payment tools to protect the people and consumers’ right to choose payment methods. Non-cash payment tools may be used if goods or services are provided through voluntary, equal, fair and honest consultations and through unmanned sales methods such as the Internet to perform legal duties and do not meet the conditions for collecting cash. Banking financial institutions and non-bank payment institutions shall not require or induce other units and individuals to refuse or take discriminatory measures to exclude cash.

3. Any unit or individual that refuses to accept or adopts discriminatory measures to exclude cash or other illegal activities shall make rectifications within one month from the date of this announcement. If the above-mentioned violations still exist after the rectification period expires, the branches of the People's Bank of China will work with relevant departments to investigate and deal with them in accordance with the law.

Official website of the People's Bank of China - Announcement [2018] No. 10 (rectification of refusal to accept cash)

Baidu Encyclopedia - "Regulations of the People's Republic of China on the Administration of Renminbi"