CONSERVATIVE-run Thurrock Council in Essex said 500 full-time jobs would have to go to make £20m of this saving.
The council cabinet decided on Wednesday to also consider selling off 33 council-owned businesses, including pubs and farmland.
Some 3,700 people have signed a petition calling for the theatre at the Thameside Complex to be saved.
Labour group leader John Kent said the Conservatives had “lost control of the finances and the cuts were an inevitable consequence of that”.
Mr Kent said whilst there would be some needed efficiencies, the loss of jobs, charges for green waste and fortnightly bin collections were inevitable.
“We just fought local elections where the Conservatives were boasting how sound the finances were and as soon as those elections are over they say everybody knew they had to do this,” he said.
In November, Thurrock Council showed it had borrowed about £1bn for investments including £604m in solar energy.
Conservative councillor Shane Hebb said its solar and green energy investments had raised “over £100m over the last four years which had enabled additional services and increased reserves by 300%”.
He argued that government imposed changes on borrowing to raise revenue meant the council could no longer continue investing in the way it had done previously.
Mr Hebb said the cuts would involve greater consolidation of services, with job losses through retirement or a review of necessity.
“We will be working smarter and leaner with some services being reformed with better use of technology,” said Mr Hebb.
Unlike other councils, Thurrock has kept council tax increases at 1.99% in recent years instead of taking advantage of the maximum annual rise of 3.99%.
Thurrock has the third lowest band D council tax compared to other unitary councils in the country and 70% of properties are in bands A to C, so raise significantly less than at Band D level.
The amount raised from council tax in 2020-21 was £69.2m compared with the nearest unitary neighbour Southend of £84.8m, figures from the council revealed.
The council’s scrutiny committees will now assess the package of savings put forward by the cabinet.