Personal relationships within a lab. What Would You Do?

Romantic relationships have developed among doctoral candidates working in a large university laboratory on several occasions. Invariably these relationships have led to bad feelings, either among those involved or among their colleagues in the lab, and productivity has suffered as a result. The director seeks to establish a policy that would sustain morale in such cases, preferably by requiring that at least one party to any such relationship must leave the lab. Is this appropriate? How should the director proceed?