1986...(article from 87)
http://articles.latimes.com/1987-02-22/entertainment/ca-4879_1_carolyn-fox
(Carolyn)Fox threw Providence into a tizzy last April Fool's Day when she announced that the fictitious Providence Labor Action Relations Board Committee had declared the city "closed for the day" and that people needn't go to work. (For people who wanted more information, she gave out the phone number of a rival rock station.) The local police said they were "swamped" with calls until Fox revealed the joke later that morning.
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From a post I did here in 2010:
http://www.museumofhoaxes.com/hoax/aprilfool/P90/
>>Carolyn Fox, a disc jockey for WHJY in Providence, Rhode Island, announced in 1986 that the 'Providence Labor Action Relations Board Committee' had decided to close the city for the day. She gave out a number for listeners to call for more information. The number was that of a rival station, WPRO-AM. Reportedly hundreds of people called WPRO, as well as City Hall and the police. Even more called into their offices to see if they had to go into work.