Employee contributions fell by 11% between the first and second quarters of 2020, while employer contributions fell 5% over the same period.
Workplace defined contribution pension membership remained the same at the end of June (23 million members) as it was at the end of the previous quarter.
Investment platform AJ Bell said the drop in contributions was likely to reflect the impact of furloughing and the financial pressure on workers' incomes during the pandemic.
Tom Selby, senior analyst at AJ Bell, said: “With the UK currently in the grip of the second wave of Coronavirus, we are now getting a clearer view of the impact the first wave of the pandemic had on people saving for retirement.
“Inevitably the national lockdown hit savers hard, with employee pension contributions down 11% and employer contributions 5% lower.
“This drop in contributions likely reflects the impact of furloughing, with total auto-enrolment contributions based on 80% of salary for millions of people. Some workers will also inevitably have opted out due to pressure on their incomes caused by the pandemic.
“Given total workplace pension membership had been increasing steadily up until March, it seems likely the figure recorded in Q2 2020 of 23 million is lower than it might have otherwise been. Membership of defined benefit (DB) schemes was also broadly stable during the period."