The unions that supported losing candidates in the September 13 primary now have another choice to make: whether to endorse Mayor Michael Bloomberg or Fernando Ferrer or just stay out of the general election race. Today the Retail, Wholesale, and Department Store Union (RWDSU)—which supported Rep. Anthony Weiner— will announce it is switching to Ferrer. Gifford Miller’s loss left several unions without a horse in the race. One of them, Local 1500 of the United Food and Commercial Workers, is still deciding. “We have not made up our mind,” says vice president Tony Speelman. “We may in fact endorse Bloomberg. We may endorse Ferrer.” The mayor, meanwhile, on Wednesday got the nod of the International Alliance of Theatrical Stage Employees, Moving Picture Technicians, Artists and Allied Crafts. According to the mayor’s campaign, it was the first time the union had picked a candidate for mayor and the first time it had ever backed a Republican.