If a company signs a supplementary agreement with an invalid official seal after cancellation, it is a case of fraudulent signing of the contract and the contract is invalid. If the circumstances are serious, it will constitute contract fraud. In any of the following circumstances, the contract is invalid:

1. One party enters into a contract by means of fraud or coercion, which harms the national interests;

2, malicious collusion, damage the interests of the state, the collective or the third party;

3. Covering up illegal purposes in a legal form;

4, damage the public interests;

5. Violation of mandatory provisions of laws and administrative regulations.

Where the person in charge directly responsible for the unit and other directly responsible personnel commit fraud in the name of the unit, the fraud proceeds shall be owned by the unit. If the amount is between 50,000 yuan and 200,000 yuan, it shall be investigated and dealt with.

legal ground

Criminal law of the people's Republic of China

Article 224 The crime of contract fraud, under any of the following circumstances, defrauds the other party of property for the purpose of illegal possession in the process of signing and performing the contract, and if the amount is relatively large, it shall be sentenced to fixed-term imprisonment of not more than three years or criminal detention and shall also or only be fined; If the amount is huge or there are other serious circumstances, he shall be sentenced to fixed-term imprisonment of not less than three years but not more than ten years and shall also be fined; If the amount is especially huge or there are other especially serious circumstances, he shall be sentenced to fixed-term imprisonment of not less than 10 years or life imprisonment, and shall also be fined or confiscated:

(1) Signing a contract in the name of a fictitious unit or others;

(2) Mortgaging with forged, altered or invalid bills or other false property rights certificates;

(three) to perform a small contract or part of the contract first, to deceive the other party to continue to sign and perform the contract, and to have no actual performance ability;

(4) After receiving the payment for goods, advance payment or secured property paid by the other party;

(5) defrauding the other party's property by other means. Article 225 Whoever, in violation of State regulations, commits one of the following illegal business operations and disrupts the market order, if the circumstances are serious, shall be sentenced to fixed-term imprisonment of not more than five years or criminal detention, and shall also, or shall only, be fined not less than one time but not more than five times the illegal income; If the circumstances are especially serious, he shall be sentenced to fixed-term imprisonment of not less than five years, and shall also be fined not less than one time but not more than five times for illegal gains or confiscation of property:

(a) operating a franchise or monopoly commodity or other commodities whose operation is restricted by laws and administrative regulations without permission;

(2) buying and selling import and export licenses, import and export certificates of origin and other business licenses or approval documents stipulated by laws and administrative regulations;

(three) without the approval of the relevant competent departments of the state, illegally engaged in securities, futures, insurance business, or illegally engaged in fund payment and settlement business;

(four) other illegal business activities that seriously disrupt the market order.