Intervenors do not need to demonstrate standing if there is a case or controversy between the parties that satisfies Article III of the Constitution.
Laroe Estates, Inc. v. Town of Chester, 15 Civ. 1086 (2d Cir. July 6, 2016) (Lohier, J.).
In reversing District Judge Edgardo Ramos's decision, the Second Circuit noted that five circuits agree and three circuits disagree with this holding, which increases the chance of Supreme Court review. A circuit split on this issue has persisted several decades and the Court has expressly declined to resolve it at least once. See Diamond v. Charles, 476 U.S. 54, 68‐69 (1986). In Diamond, the Supreme Court held only that if the original party in the litigation on whose side intervention occurred does not appeal but the intervenor wants to appeal on its own, then the intervenor must satisfy Article III’s standing requirement. See id. at 68.
Second Circuit decision: http://cases.justia.com/federal/appellate-courts/ca2/15-1086/15-1086-2016-07-06.pdf?ts=1467813611
District Court decision: https://cases.justia.com/federal/district-courts/new-york/nysdce/1:2012cv00647/413647/39/0.pdf?ts=1427977074
Intervenors Still in Limbo on Standing Requirements By Renee Choy Ohlendorf, Litigation News (March 26, 2012): https://apps.americanbar.org/litigation/litigationnews/top_stories/032612-intervenor-circuit-split.html
Juliet Johnson Karastelev, On the Outside Seeking In: Must Intervenors Demonstrate Standing to Join a Lawsuit?, 52 Duke L.J. 455 (2002): http://scholarship.law.duke.edu/cgi/viewcontent.cgi?article=1175&context=dlj
Elizabeth Zwickert Timmermans, Has the Bowsher Doctrine Solved the Debate?: The Relationship Between Standing and Intervention As of Right, 84 Notre Dame L. Rev. 1411 (2009): http://scholarship.law.nd.edu/cgi/viewcontent.cgi?article=1218&context=ndlr