The Movement For Credible Cycling (MPCC) has said the lower number of anti-doping tests conducted in 2020 is a "great source of worry".
The MPCC is a union, including seven of the 18 International Cycling Union (UCI) WorldTour teams, and seeks to defend the image of cycling through "transparency, responsibility and mobilisation of its members".
A statement from the group expressed concern over the impact of the coronavirus pandemic on the anti-doping system.
Twelve positive cases have reportedly been confirmed in cycling, between January 1 and October 1.
"The World Anti-Doping Agency (WADA), through its general director Olivier Niggli, conceded a few days ago that the pandemic may have created some 'holes' in the anti-doping programmes in several countries," the MPCC said.
"Multiple international federations agree with this unpleasant statement.
"The Cycling Anti-Doping Foundation (CADF) admitted a 90 per cent decrease in out-of-competition tests during the two months following the start of the pandemic compared to the same period last year.
"Across all sports, we logically account for a lower number of cases than during the previous years.
"There is one notable exception: track and field, where almost 100 cases have been revealed throughout the first three quarters of the year 2020 (as against 81 cases during the whole year 2019).
"Within the same period, cycling had to deal with a dozen cases (two within World Teams), a lower figure than last year at the same time, but still very close to the data of the last five years.
"This last observation is a great source of worry for MPCC, given the lower number of tests in 2020."
The 12 positives in the sport reportedly include nine in road cycling, one in BMX, one in mountain bike and one in track cycling.
The CADF reported in September that its testing programme had returned to normal levels, following the drop caused by the pandemic.
It had also announced in June that the pandemic had led to a significant reduction in its activity, in accordance with WADA and Government guidelines.
Many cyclists in the testing pool had been residing in nations with strict limits on movement and physical interactions in place.
The CADF said out-of-competition tests fell by 90 per cent as a result.
During March and April, the CADF said it had collected almost as many samples from cyclists as all National Anti-Doping Organisations combined.
Testing has now resumed across the world amid the return of sports events, and figures published by WADA during its Foundation Board meeting earlier this month showed the number of samples collected in September was around 80 per cent of the figure recorded for the same month in 2019.
WADA said more than 18,500 samples had been collected in September, an increase of around 4,000 compared with August.
With some areas struggling to cope with a second wave of coronavirus, concerns have been raised that the introduction of further restrictions could again impact anti-doping.
WADA has repeatedly highlighted that testing is not the only way drugs cheats can be caught, although there are fears that some athletes may have tried to exploit the reduced system.