To write the exponential equation in logarithmic form, you can use the definition of a logarithm. The logarithmic form of the equation \( \log_b a = c \) is equivalent to the exponential form \( b^c = a \).
Given the equation:
\[ \log_3 \frac{1}{27} = -3 \]
This can be rewritten in exponential form as:
\[ 3^{-3} = \frac{1}{27} \]
Thus, the equation you are looking for is:
\[ 3^{-3} = \frac{1}{27} \]