The site is the latest battleground in a row over pay and conditions which has seen sparks and major M&E contractors at loggerheads.
T Clarke is one of eight leading contractors planning to pull out of the industry’s JIB agreement.
The other breakaway contractors are Bailey Building Services, Balfour Beatty Engineering Services, Crown House Technologies, Gratte Brothers., MJN Colston, SES and SPIE Matthew Hall.
Balfour Beatty and NG Bailey have already seen sites targeted as rank-and-file electricians vow to spread their protests across the industry.
Westfield is another high profile job and today’s demonstration will raise fears that sparks could soon turn their attention to the neighbouring Olympic Park.
A source at one employer said: “Obviously it’s not ideal to see demonstrations like this but we don’t believe these protesters are representative of most site M&E workers.
“We are confident that when workers see that they won’t lose out under our proposals they will move to back this much needed modernisation of the industry.”