for contracts. In 1971, a 53-day strike among Yale employees was the longest in the school's history. Union leaders stated that they considered Yale's social commitment to New Haven to be a key issue in the job action. University workers in New Haven would strike again and again in the 1970s, 1980s, and 1990s. Historically, over half of all college students in the U.S. have lived independently off campus. However, in communities where institutions have expanding enrollments and insufficient housing for their students, the competition between students and residents for off-campus student housing has become a common source of friction in town-gown relations. Municipalities and universities continue to negotiate police jurisdiction on and near campuses. Today, many universities and colleges maintain their own police forces. In cities where a significant number of students live off campus, university police may be allowed to patrol these neighbourhoods to provide an extra measure of security. Meanwhile, civil libertarians argue that school officials should only call on local law enforcement to intervene when it is necessary to protect the safety of people on campus. Such intrusion is legally mandated in some jurisdictions when school officials have reasonable suspicion to believe that a student is breaking the law. Generally, local police are reluctant to go on campus if a college maintains its own security force (the Kent State and Jackson State killings are examples of intervention turning into tragedy). Raucous off-campus parties and the excessive noise and public drunkenness associated with them can also create town–gown animosity. The University of Colorado (Boulder, Colorado, USA) and Queen's University (Kingston, Canada) provide examples where street parties have escalated into riots. In 1995, at Wilfrid Laurier University in sedate Waterloo, Ontario, the "Ezra Street riot" occurred when 1500 revellers showed up at an end-of-the-year student party on Ezra Street. The party goers drank copious amounts of beer, threw bottles, and carried on in ways that resulted in 42 arrests and two serious injuries – one when a woman was hit by a chunk of concrete thrown at the party, the other when a man was run over by a jeep. The end result was the university's adoption of a new "Code of Conduct" to govern student behaviour. In the 1970s and 1980s, attention was often focused on off-campus fraternities and sororities, whose sometimes rowdy events were lampooned in the 1978 film Animal House. Ironically, the institution of "social