Final answer:
When a law involving a suspect classification or fundamental right is challenged, strict scrutiny or intermediate scrutiny standards are applied, depending on the case. The government must prove the necessity and compelling interest of the law under strict scrutiny, while the challenger must prove substantial relation to an important government interest under intermediate scrutiny. The rational basis test is used for laws that do not involve suspect classifications or fundamental rights.
Step-by-step explanation:
When a law that involves a suspect classification (such as race or religion) or a fundamental right (such as the right to travel) is challenged, a strict scrutiny standard is applied—the government must prove that the law is necessary to achieve a compelling government interest. Under strict scrutiny, the burden of proof is on the government to demonstrate that there is a compelling governmental interest in treating people from one group differently from those who are not part of that group, the law or action can be "narrowly tailored" to achieve the goal in question, and that it is the "least restrictive means" available to achieve that goal.
On the other hand, when discrimination based on gender or sex is challenged, an intermediate scrutiny standard is applied. The challenger must prove that the law is substantially related to an important government interest. This means that the burden of proof is on the challenger, not the government.
If the law does not involve a suspect classification or a fundamental right, the courts apply the rational basis test. Under this test, as long as there is a reason for treating some people differently that is "rationally related to a legitimate government interest," the discriminatory act or law or policy is acceptable.