Glasgow Life, which runs the city's sport and leisure facilities, is changing the opening times at the city's 33 libraries.
On average, comm-unity libraries will be available for three hours fewer each week - or 30 minutes per day.
A spokesman for the arm's-length council company said the changes would stand-ardise opening hours across the city.
Some libraries will open later or close slightly earlier, with savings being invested in new or improved services, the spokes-man added.
An assessment of opening hours shows many libraries are opening too early or too late and not meeting demand.
New plans will see 20 community libraries open for 48 hours per week, and nine open for 42 hours per week.
Worst hit will be Gorbals library, which will lose 12 hours. Bridgeton and Car-donald will see their weekly hours reduced from 53 to 48.
Hillhead Library will open for 59 hours, The Bridge, in Easterhouse, will open for 57 and the library in GoMA will stay open for 50 hours.
Glasgow Life said the standardised hours will help staff to deliver better services and improve working conditions by allowing more regular hours for staff.
The organisation said it is in talks with unions to discuss new changes.
A spokesman for Unison said: "We have been told about the plans and are currently in dialogue with Glasgow Life to find out what impact this will have on staff."
The organisation said it also plans to invest in welfare reform support, digital learning, programmes for families, children, young people and adults, and information services.
The report shows it also intends to expand health information schemes, such as the current partnership with Macmillan Cancer Support.
A spokesman for Glasgow Life said: "Libraries are at the heart of our commun-ities and in Glasgow the service consis-tently scores around 90% satisfaction in household surveys.
"Glasgow Life is looking to build on that success by developing new services that will benefit the lives of both individuals and communities. This comes at a time when, in other parts of the UK, library services and provision have been under pressure due to cuts to public funding.
"Some libraries have been closed or trans-ferred into community ownership.
"In Glasgow, there have been no library closures and none are planned."
The move comes as changes are being made to welfare reform that will see all benefit claimants make and manage their claims online.
Libraries will offer support to those who do not have access to a computer, putting extra strain on the service.
Glasgow Libraries is the largest network of public libraries in Scotland, with 32 community libraries and the Mitchell.
The service has had 5.5 million visits and 1.1m usages of PCs and Wi-Fi in the past year. Customers can access online facilities 24 hours a day, resulting in 1.2m virtual visits.
New opening hours will be put into place by April 21, depending on the outcome of a Glasgow Life board meeting next week.