In this paper we study the Nielsen identity for the supersymmetric
Chern-Simons-matter model in the superfield formalism, in three spacetime
dimensions. The Nielsen identity is essential to understand the gauge
invariance of the symmetry breaking mechanism, and it is calculated by using
the BRST invariance of the model. We discuss the technical difficulties in
applying this identity to the complete effective superpotential, but we show
how we can study in detail the gauge independence of one part of the effective
superpotential, Keff. We calculate the renormalization group functions of
the model for arbitrary gauge-fixing parameter, finding them to be independent
of the gauge choice. This result can be used to argue that Keff also does
not depend on the gauge parameter. We discuss the possibility of the extension
of these results to the complete effective superpotential.Comment: v2: 23 pages, 4 figures, version accepted for publication in PR