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Aretha Franklin's son says the rep who controls his mother's estate is on a spending spree -- with the singer's fortune -- and he wants a judge to put a stop to it ... stat.

Aretha's son, Kecalf Franklin, wants a judge to grant a temporary restraining order against the estate's rep, Sabrina Owens ... barring her from making any decisions on behalf of the estate until the court decides whether Owens -- who is also Aretha's niece -- should even have that authority.

Kecalf claims Sabrina has sold property, personal items and spent money to advertise the items for sale. Kecalf also says Sabrina transferred a car to her name and received money on behalf of the estate ... though he doesn't name a specific amount.