The Buddhist monk Saichô (767-822) dared to abrogate the multitude of traditional small precepts in favour of the sole precept to «awaken to the fundamental one-mind of Mahayana». He established a ceremony for the taking of this precept and built a Mahayana ordination platform for the purpose on Mount Hiei near Kyoto. Since then, various branches of Japanese Buddhism have adhered to this. But Zen, following in the steps of its Chinese tradition, upheld an original structure of mutual complementarity of the monastic and secular communities and thus did not completely give way to lay Buddhism. Although this was a contradictory compromise of a kind that is again different from that of Southeast Asian Buddhism, one can say that the realization of this kind of contradiction bears potential for the future. However, it also proved to be a cause for confusion in monastic Japanese Buddhism.There's another account here Monks, Nuns & Priests in Western Zen
From: the View of a Zen Monk from Japan - read it to get more of an understanding of the Zen view on ordination.