Usually that would be controlled under Tools -> Beautify -> Edit Current Profile, under Spacing -> Statements, and then click on the statement type and look for the "Pad inside parenthesis" setting.
The exception to that is if you have adaptive formatting enabled - in that case, if adaptive formatting has decided that you're padding parens in control statements, that would also enable it. You can check if that's the case by running "adaptive-format-stats" in the SlickEdit command line, and seeing if it made a decision about paren padding.
If those aren't it, may need to do some debugging.