Demonstrators are planning to picket the entrance to the Grosvenor House hotel where the ECA is hosting its annual do.
More than 1,000 industry guests are expected at the £105-a-head event where former London mayor Ken Livingstone is guest speaker.
The demonstration is the latest round of protests against plans by leading M&E contractors to replace the JIB pay and conditions agreement with a new deal known as BESNA.
Protest organisers said the dress code for the demonstration will be “casual chic, with maybe the odd hard hat” while ECA guests will be in black-tie.