documentclass{article}


usepackage{cleveref}
usepackage{cases}


begin{document}

section{Intro}

begin{numcases}{}
 a=b \
 c=d. label{c=d}
end{numcases}

Cleveref produces a reference to the section: cref{c=d}

Regular ref produces a reference to the equation: ref{c=d}.
end{document}

% arara: pdflatex
% arara: pdflatex

documentclass{article}
usepackage{empheq} % loading `mathtools` % loading `amsmath`
usepackage{cleveref} % load this as very last package

begin{document}
    section{Intro}
    begin{empheq}[left={=empheqbiglbrace~}]{align}
    a&=b\
    c&=dlabel{eq:equation}
    end{empheq}
    Cleveref produces a reference to the section: cref{eq:equation}

    Regular ref produces a reference to the equation: ref{eq:equation}.
end{document}