I purchased an apartment in 2007 with a designated communal washroom. Yesterday at the house meeting the majority voted to get rid of the washroom and create a second ski room (saying allowing continued washing will rust the skis). Both myself and another owner depend on the washroom. Can such a drastic change be made by a majority vote?

What does your contract say?

Google for: stockwerkeigentum beschluss anfechten

Will any washing facilities remain after this change or is expected that everyone must have an own washing machine in their apartment ?

The claim that skis will rust is rather odd. It also indicates an acceptance that the washing facilities are currently being used (no washing, no steam, no rust) and the metal parts of modern skis are anyway usually of stainless steel.

Normally there is a law on this, stating what can be agreed with a majority vote, what needs a 100% vote. In Germany it is called WEG Gesetz, maybe check if there is something similar in Switzerland?

(My stupid DDG only shows me German links, sorry).....