I just read on the SBB site that travel to Brig & Zermatt from Gevena Airport (on the southern route through St Maurice) requires a bus reroute service until June 27th.
From the website:
http://www.sbb.ch/en/home.html
Construction work: St-Maurice (SBB CFF FFS)
Construction work: Train services at St-Maurice station are suspended. Long-distance trains IR
14xx + 17xx Brig - Genève-Aéroport are cancelled between St-Maurice
and Bex. Regional trains R 44xx Brig - St-Maurice - Monthey are
cancelled between St-Maurice and Monthey. Replacement bus services are
operating St-Maurice - Bex + St-Maurice - Monthey. The bus/train
connections are guaranteed in St-Maurice, Bex + Monthey. Please allow
for approx. 15 - 20 minutes more travel time. Duration of construction
work from 15.06.2014 until 20.06.2014 from 22:40 until close of
services. Duration of construction work from 22.06.2014 until
27.06.2014 from 22:40 until close of services. Please listen to the loudspeaker announcements in the train. Please note the information at
the station.