The two conservative justices on the nine-member court dissented and wanted to take the case. Justice Clarence Thomas wrote a six-page dissent on the issue arguing that the majority of owners use them for lawful purposes.
"Under our precedents, that is all that is needed for citizens to have a right under the Second Amendment to keep such weapons," he argued.
The 7th Circuit Court in Chicago had previously rejected the ordinance as well, despite much rallying by the NRA for the courts to hear the case.
Lawyers from Highland Park pointed to mass shootings across the nation as well as the fact that seven states currently have similar bans.
Democrats have been lobbying even harder than normal for the past week, as mass shootings continue to happen more than daily throughout the country.
In a speech from the Oval Office on Sunday evening, President Barack Obama continued to call for a ban on assault rifles.
“We also need to make it harder for people to buy powerful assault weapons like the ones that were used in San Bernardino. I know there are some who reject any gun safety measures. But the fact is that our intelligence and law enforcement agencies — no matter how effective they are — cannot identify every would-be mass shooter, whether that individual is motivated by ISIL or some other hateful ideology. What we can do — and must do — is make it harder for them to kill,” he stated.