That sounds a bit like BS to me.
If there's a penalty for taking a practice swing on a tee, then slap me with 9 penalties per 9 holes.
Almost every member of our social club will have a practice swing on the tee.

Page 54- RULES OF GOLF as approved by R&A Rules Limited and
The United States Golf Association
http://www.randa.org/flash/rules/PDF/RoG2004.pdf
Note 1: A practice swing is not a practice stroke and may be
taken at any place, provided the player does not breach
the Rules.

Cheers

Darran