Regina Weigand, a spokeswoman for Sun in Europe, said: "Sun saves significant costs when people take vacation. The company is obliged to set aside money for accrued holiday days."
Weigand added that unlike their European counterparts, all US-based Sun employees were permitted to carry accrued holidays over into the following year.
This is the second time this year that Sun has asked its employees to take a week's leave. In early August the company announced that it intended to reduce its workforce by 300 through what it called a "redeployment programme".
Sun has so far avoided the large-scale lay-offs announced by other hardware makers such as Dell, Hewlett-Packard and Compaq.