It is recommended that you redefine your own modulus operator or use the below structure as the output from the commands is not read correctly by a screenreader on transformation.
$a~\mathrm{mod}~b$, $a~ (b)$
$a~ \mathrm{mod}~ b$, $a~ (b)$
The following are not read correctly:
$a \mod{b}$, $a \pod{b}$
$a \mod {b}$, $a \pod {b}$