Councils reduced funding for libraries by a total of £25m in the last financial year, research has found.
The Chartered Institute of Public Finance and Accountancy analysis revealed investment in libraries across Great Britain fell from £944m in 2014-15 to £919m in 2015-16.
The total number of libraries in Great Britain fell from 3,917 to 3,850 during the same period.
Cipfa said a 5.3% reduction in the number of paid library staff coincided with a 7.5% increase in the level of volunteers.
The research highlighted the continuation of year-on-year decreases in council spending on libraries since 2010.
Chief executive Rob Whiteman said “tough decisions” had to be made at a time of “unprecedented budgetary pressures”.
He added: “But despite the grim outlook, libraries are continuing to transform and innovate, adapting to changing visitor habits and providing a raft of new services and offerings.”
Last week, the Government’s Libraries Taskforce pledged £4m to support disadvantaged communities through libraries.
The Cipfa research found Birmingham Library was the most visited library in the country, with 1.6m visitors in 2015-16.
The library offers adult learning facilities, immigration advice services and supplements its funding through private hiring.