By SAM HANANELWASHINGTON (AP) â¿¿ An overnight fire at the Labor Department's headquarters shut the building down for most employees early Friday, but the agency's monthly employment report was released as scheduled. Department employees and members of the news media involved in the release of the report were allowed in the building as usual. But all other Labor employees who were scheduled to work in the Frances Perkins building received administrative leave. District of Columbia fire department spokesman Lon Walls said the fire was reported around 4:35 a.m., but the sprinkler system extinguished it before firefighters arrived. He said the cause is under investigation. Labor Department spokesman Carl Fillichio said the fire was in a cubicle on the fourth floor, and the fourth, third, second and plaza levels on the north side of the building were affected by water. Employees in the unaffected areas were allowed to return. The building on Constitution Avenue opened in 1975. The April jobs report showed unemployment hitting a four-year low, with employers adding 165,000 jobs in April and upwardly revised figures for the previous two months.