Members of the GMB Union staged a demonstration near to the Treasury in a last-ditch plea to the Chancellor to give public sector workers a pay rise in the Budget.
The masked "Maybots", made to resemble Prime Minister Theresa May as a robot, were joined by a Chancellor figure on Wednesday morning - just hours before Mr Hammond was due to make his much-anticipated speech.
Unions have been pressing the Government for months to scrap the cap on the pay of millions of public sector workers.
The union, which represents 640,000 public and private sector workers, urged the Chancellor to "end seven years of misery" for the industry.
The masked demonstrators were joined by a 'Gothic Chancellor' in a dark mask shaped like a crow.
GMB national officer Rehana Azam said: "Today the Chancellor can end seven years of misery for our 5.5 million public sector workers.
"Seven years where they've had their real terms pay slashed, leaving them forced to use food banks while struggling to pay the rent and feed their families.
"People are sick to the back teeth of austerity - while the richest in the country enjoy tax cuts.
"If this Government can find £40 billion to leave the EU, and £1.5 billion to keep themselves in power, they can find the money to lift the pay cap for our millions of public sector workers."
Protests took place on College Green, Westminster Abbey, and outside the Treasury.