Final answer:
A state regulation that requires firefighters to be men is subject to intermediate scrutiny, which demands the government to show that the gender-based requirement is substantially related to an important governmental objective and is an appropriate method for achieving that objective.
Step-by-step explanation:
The state regulation requiring firefighters to be men because of the demanding physical requirements would be examined using intermediate scrutiny. This level of scrutiny requires the government to prove that the gender-based classification is substantially related to an important governmental objective. Since gender discrimination is being discussed, it is not sufficient for the state to show just any rational basis for the law; instead, there must be a clear, significant justification for why the law treats different genders unequally. This approach aligns with precedents set by the Supreme Court in cases such as Craig v. Boren and Clark v. Jeter, which outline that distinctions based on gender must serve an important governmental goal and that the discriminatory means employed must be closely related to achieving that goal. As such, a law that only allows men to be firefighters based solely on physicality would likely fail to meet the intermediate scrutiny standard unless the government can provide compelling evidence to justify this exclusion.