When I go to Beijing to stay in a hotel, my friends always ask me to write out their company's invoice (tax number). Is it illegal?

It may be suspected of breaking the law and it is recommended to handle it with caution.

If you spend it yourself but invoice the value-added tax in the name of your friend, it is illegal, because your friend has no real consumption behavior, which is a false invoice.

Invoice refers to the business vouchers issued and collected by all units and individuals in buying and selling goods, providing or receiving services and engaging in other business activities. It is the original basis of accounting, and it is also an important basis for law enforcement inspection by audit institutions and tax authorities.