Which? said the rate of closures cast “serious doubt” on promises by the network operator, Link, to protect access in country areas.
The findings come ahead of changes to the way the network is funded, which come into effect at the weekend.
Link is to cut the fees operators receive from banks when machines are used – but some in the industry have warned that thousands of free machines could be removed or become fee-charging, with “cash deserts” created across the UK.
Link said there would be a phased reduction in the fee that card issuers pay to machine operators, starting next week.
It said the effect was expected to be “a modest decline” in the number of machines in areas of heavy concentration but with “no diminution in the overall geographical coverage”.
But Which? found that nearly 1,500 machines closed between last November and April, which it said was a near six-fold increase from a steady rate of fewer than 50 closures a month since 2015.
It said such closures would hit rural communities especially hard at a time when bank branch closures were also gaining pace.
Which? Money editor Harry Rose said: “We have serious concerns that, far from protecting consumers’ access to cash, Link’s plans risk destroying it.
“The regulator must act now to stop further closures.”