How about something like:
\documentclass{article}
\usepackage{amssymb,amsmath}
\begin{document}
\begin{equation}\label{A_Label}
\begin{split}
w^T x_i + b \geqslant 1-\xi_i \text{ if } y_i &= 1, \\
w^T x_i + b \leqslant -1+\xi_i \text{ if } y_i &= -1
\end{split}
\end{equation}
\end{document}
which produces:
