The Financial Conduct Authority (FCA) needs to offer its staff a better pay package or it risks becoming unable to deliver in the public interest, union Unite said.
The FCA, which regulates the conduct of around 50,000 financial services businesses, has been in dispute with its workers over pay and conditions.
It said it told staff on Tuesday it expects them to receive, on average, a base salary increase of 6.5% this year.
But Unite said FCA management has refused to discuss pay and morale with workers, leading to unhappiness and hundreds leaving in the past 18 months.
It is pushing the regulator towards “breaking point” and calls its ability to keep consumers safe into question, the union said.
While around 650 staff left the business last year, it hired more than 1,130, it said.
In a letter to FCA chief executive Nikhil Rathi, Unite regional officer Steve O’Donnell said: “We are writing to you following your decision to impose a pay deal for 2023 that fails to meet the rising costs of living and your failure to consult staff at any point in reaching this decision.
“Because of the failure by your management to give the workforce a say on pay – Unite the Union has had to.”
Mr O’Donnell added: “Already over a fifth of FCA staff have left in the last year alone. These staff are being replaced by less experienced yet more expensive new joiners.
“Unite the Union is clear that without significant investment in your staff now, more staff will leave, and the FCA stands at the precipice of crisis.
“The reality is that on your current trajectory, the public can no longer have confidence in the FCA’s ability to deliver in the public interest.”
The union said it wants to see base pay increased in line with inflation and regardless of performance grades.
The FCA said staff earning less than £125,000 a year and meeting performance targets will see a salary rise of at least 4.5%, while those earning more than £125,000 will get a 4% minimum pay rise.
In the last two years, staff pay has gone up by 14% on average, the FCA said.
A spokesman added: “We continue to provide one of the best overall employment packages of any other regulator or enforcement agency in the UK.
“We attract a high calibre of talent, and we’ve successfully recruited more than 1,000 new colleagues over the last 12 months as our headcount grows to meet an expanding remit.”
Unite conducted a survey of 500 members and non-members of the union working across the FCA this month, including staff at every level and department and its offices across the UK.
It found 87% of staff were dissatisfied with the employee offer set out last April, while 62% believe they are not paid fairly for their work.
More than half of employees are actively looking to leave the FCA, Unite’s survey found.
Staff at the regulator in Edinburgh went on strike in May for the first time in its nine-year history.
Unite said at the time that Edinburgh-based workers were worse off than their London-based colleagues despite doing the same job.