It kind of depends on who does the reporting --
some of the details change in the telling.

According to the Boston Globe,
it is thirteen, not sixteen, other states getting read
to ask the US Supreme Court to stop Massachusetts' "egg law."

The thirteen are
Texas
Utah
Oklahoma
Nebraska
North Dakota
Arkansas
Missouri
Wisconsin
Indiana
Alabama
Louisiana
West Virginia
South Carolina

(odd that Iowa is not on the Boston Globe's list)

The same Boston Globe Article dated 11 December
says that the actual deadline -- here's the quote --
"set to take effect in 2022."
That's their interpretation.