A more thorough explanation:

The Tax Injunction Act is a federal law that prevents federal courts from interfering with the assessment or collection of any state tax, as long as the state provides a quick and effective way to resolve any disputes related to the tax in its own courts. This law is found in 28 USCA § 1341.

Let's say that a business owner in California believes that they have been overcharged on their state taxes. They could file a lawsuit in federal court to challenge the tax assessment. However, if California has a process in place for the business owner to dispute the tax assessment in state court, the Tax Injunction Act would prevent the federal court from getting involved.

The purpose of the Tax Injunction Act is to avoid federal courts interfering with state tax systems and to allow states to handle their own tax issues without federal interference.