I think you managed to extract only part of the complete phrase. I suspect there is another word: commerce. There are cases that involve interstate commerce. I found a Supreme Court case entitled:
Corn Products Refining Co. v. Eddy, 249 U.S. 427
The second paragraph contains the phrase:
. . . defendants were interfering with plaintiff's interstate commerce and with its lawful business in the state of Kansas, thereby threatening plaintiff with great and irreparable damage . . .
You can read the full case at the related link.
Interstate commerce is commercial trade that takes place between states and over state lines and is regulated by federal law and therefore under federal jurisdiction when there is a lawsuit filed or violation of law.
To refer to two plaintiffs without indicating possession, you would write "two plaintiffs" or "2 plaintiffs." This form does not suggest ownership or possession.
The plural possessive form, plaintiffs'consent, is the correct form for the consent of the plaintiffs.
Pertaining to the mutual relations of States; existing between, or including, different States; as, interstate commerce.
If you are talking about one plaintiff, then it is: Plaintiff's Complaint. If it is the complaint of many plaintiffs, then it would be: Plaintiffs' Complaint.
interstate high way system
The plural form of plaintiff is plaintiffs.
the meaning of the phrase myriad manifestation is-countless evidence
The correct possessive form of "Plaintiffs" is "Plaintiffs'." This is because the word "Plaintiffs" is already a plural noun, so to indicate possession, an apostrophe is added after the final "s." Using "Plaintiffs's" would be redundant and incorrect in standard English grammar.
You may be seeking the phrase "interstate commerce."
A phrase that is compound. Meaning two or more.
That's easy! Its a phrase.
The plural form of plaintiff is plaintiffs.