The Financial Conduct Authority’s Unite members took part in the first day of strike action and held placards and flags complaining about changes to pay and conditions of employment.
Unite told FTAdviser it could not confirm the numbers of those striking at this stage as most were still working at home and striking remotely.
It said the numbers on the picket were "just a handful" of those taking action.
The FCA has said its employment package is "highly competitive" and that most employees will receive an average 7 per cent pay rise this year.
The strike comes after members of Unite, the union which represents staff at the regulator, agreed last month to take part in a work-to-rule, meaning they would work strictly to their contracts of employment, job descriptions and working hours.
Today (May 4), members of Unite began the strike outside the FCA’s London office at 8.45am in action which will continue tomorrow.
Strikers held placards, flags and leaflets urging the FCA to listen to its staff. They held signs reading ‘FCA don’t take our pay’ and ‘FCA staff ignored too long’.
Sharon Graham, Unite general secretary, said: “Unite members at the Financial Conduct Authority must be congratulated for taking a stand against the disgraceful actions of the management under the leadership of the chief executive, Nikhil Rathi.
“The imposition of changes to pay, terms and conditions at the FCA has left thousands of staff worse off. Management’s ludicrous claims that the changes will boost worker productivity has only added insult to injury.
"And then by refusing to recognise the right to an independent trade union, they have really shown the depths to which they are prepared to sink. It is frankly disgusting that a public sector employer like the FCA thinks it can behave with such contempt towards its workers.
“Nobody takes industrial action lightly and this is the first strike in the history of the FCA. The FCA must learn to respect its workers and table a serious offer.”
The action will include 48 hours of continuous strike action by workers across the financial regulator in London and Edinburgh.
This will be followed by a continuous ‘work to rule’ by the workforce who will withdraw the regular overtime and additional work they currently do outside of their contractual duties.
Unite has claimed both the industrial action and the work to rule will have a significant impact on the ability of the FCA to conduct its regulatory responsibilities and damage the standing of the organisation.
A spokesperson for the FCA said: “Our new employment package is highly competitive, providing fair, competitive pay at all levels and rewards strong, consistent performance. Most colleagues are receiving an average 7 per cent increase in base pay this year and over 12 per cent over the next two years, with an additional one-off cash payment of 4 per cent in May.