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Quoting from (click link >) ITTF statutes book

ITTF Rule 2.4.7 The racket covering shall be used without any physical, chemical or other
treatment

ITTF Regulation 3.4.2.2 The racket covering shall be used as it has been authorised by the ITTF
without any physical, chemical or other treatment, changing or modifying
playing properties, friction, outlook, colour, structure, surface, etc.; in
particular, no additives shall be used.

However please note that this ban only exists to fool the IOC into thinking that Olympic Table Tennis is a healthy sport.
This ban in reality however is hardly enforced especially at lower levels, where there is zero chemical testing but ITTF and its umpires aggressively bully pips players because much smaller number of players treat their pips.
There are about 100 to 200 spien glue & booster cheats for every pips treat cheat . Yet ITTF and its umpires focus on aggressively bullying pips players because it is much easier to visually examine rubbers & it makes it look like umpires doing heir job. But the problem is that testing for spein glues and boosters is a serious health issue and has a much higher priority but it is hardly ever tested for at lower levels. In fact some umpires may not even be aware of the fact that spein gluing and boosting serious health epidemic in table tennis