On 14 October 1762, a decision taken by the State Council was expected to put an end to a decades-long sanitary and economic struggle between French Mediterranean ports while the memory of the last great plague outbreak of 1720 in Provence remained vivid. At the time, Marseille seemed considerably reinforced by the royal decision that obliged every person and good from the Levant and North Africa to stop for quarantine checks in the Phocaean city. In fact, the 1762 royal decision marked the beginning of a fierce dispute led by the Norman elites of Le Havre against a Marseille’s monopoly that could eventually deprive them of any trade with the Mediterranean in the context of renewed corsair activity around Gibraltar. Encouraged by local and provincial authorities alike, these protests never managed to win Versailles’ support and ultimately failed to overrule the decision acted in 1762. Beyond this initial assessment, the close analysis of the power dynamics at work reveals how the Norman seaports actively circumvented the legal constraints. The quarantine issue at Le Havre in the second half of the eighteenth century neatly demonstrates relationships made of negotiation and opposition between the multiple political and administrative powers in the kingdom and the strong competition between Mediterranean and Atlantic ports to establish a maritime hierarchy. Ultimately, the study of Le Havre’s “Marseille issue” sheds new light on a neglected aspect of the modern state’s construction in the last years of the Ancien Regime.