On pure Emacs:

open some buffer M-s-o for occur
then e for occur-edit-mode, then M-x replace-regexp [ ^I]+ RET SPC RET
;; try to replace excess spaces or tabs by just one space symbol in matched strings

Error in minibuffer => Wrong type argument: markerp, nil
OS X, Emacs 24.3

Best regards,

Yuriy Pitomets