Few conferences allow to use separate font size for bibliography. Here is how you can set a different font size for Reference section alone. Place following command before bibliography section:

\def\bibfont{\footnotesize}

You should make sure that you use appropriate command in place of footnotesize e.g., small, large. For example if size of the body text is set to 10pt then footnotesize size will be 8pt. More information about the footnotesize size can be found here.