At the beginning of this month, Unite wrote to FCA boss Nikhil Rathi criticising the City watchdog's new pay package which was put together without consulting staff.
The package will see employees below senior management level receive a minimum 4.5 per cent pay increase, but the FCA has said the average uplift is closer to a 6.5 per cent.
In a letter responding to Unite, the regulator's chief people officer Siobhán Sheridan said: "In the last three months we have seen a sustained drop in the number of leavers and the leaver data we have suggests that this level looks set to continue over the next three months.
"If we project forward and consider this on an annualised basis this would suggest we are currently seeing attrition at a rate of around 10-12 per cent which is broadly in line with what we saw at the FCA prior to the pandemic."
Sheridan said staff turnover "fell sharply" during the period of the pandemic and then rose afterwards. Its voluntary turnover rate was 16 per cent on a 12-month rolling basis as of January 31, 2023.
Headcount at the FCA reached 4,352 last month, from a full-time headcount of 3,878 at the end of March 2022.
Some 1,136 colleagues joined the FCA in 2022, a year which saw 649 staff exits.
The regulator expects headcount will continue to grow, with at least a further 150 new joiners expected before the end of March 2023.
This would take its total number of employees to about 4,500.
In January, the FCA proposed to add two union members to its internal staff consultative committee (SCC) in response to feedback from employees.
The FCA said while it did update the SCC on its latest pay package, it did not conduct a consultation like it did last year.
In her letter to Unite, Sheridan said the package was an "update" of the original commitments made in its 2022 employment offer which was consulted on.
"Looking ahead, we expect to have a clear agreement on how we will involve the enhanced SCC, including FDA [Union] and Unite staff representatives on these matters in time for next year's pay review," Sheridan said.
"I look forward to working together jointly to continue to ensure we retain and attract the people with the skills and values we need to deliver our strategy over the long term, protecting consumers and ensuring market integrity."