Activists will dress up as highway robbers, carrying banners saying "The Great British Royal Mail Robbery" to mark Vince Cable's session before the Business, Innovation and Skills Committee.
The minister will face questions on the valuation of Royal Mail, including whether or not it has been undervalued by the Government, details of the employee share scheme, protection of the universal service, and the value of company assets, including the Nine Elms site in south London
The meeting will be held following the deadline for buying shares, at midnight tonight, with conditional trading starting on Friday and full trading next Tuesday, a day before the result of a strike ballot by the Communication Workers Union (CWU).
Labour and the unions have warned the Government it is selling the postal operator too cheaply, amid predictions of huge profits by investors.
CWU members are expected to back industrial action over issues linked to privatisation, with any strike set to be held on or after October 23 - the run-up to the busy Christmas period.
Mr Cable has warned Labour that its opposition to the sale was "irresponsible", adding it was "dangerous" to imply there was an easy bargain to be made.