A summary of the brief provided to ABC News shows the states will argue that their "funeral picketing/protest" laws are constitutional because of an expected right to privacy at a burial and because mourners are a "captive audience" to their dead, leaving them little choice but be subjected to the message of protesters.
"Parents, siblings, family, close friends, and neighbors cannot be expected to skip a loved one's funeral in order to avoid the malicious and intentionally hurtful messages the Phelpses love to use to target mourners," the summary reads.
The Supreme Court agreed to hear the case earlier this year on appeal by Albert Snyder, Lance Cpl. Snyder's father.
Snyder first sued Phelps and his congregation claiming that their protest at his son's private funeral was an invasion of the family's privacy and inflicted emotional distress.
A U.S. district court ruled in Snyder's favor and awarded a judgment of $5 million. But a federal appeals court overturned that decision, finding that the protest signs weren't aimed at Snyder specifically and said the statements are "protected by the Constitution."
"We are constrained to agree that these signs are entitled to First Amendment protection," the three-judge panel wrote.
The Supreme Court will hear oral arguments in the case in October.
ABC News' Matt Loffman contributed to this report.