Work includes improving disabled access, baby changing facilities and new customer interview spaces.
Opponents say the work is inappropriate when the council is closing public toilets and increasing parking charges.
The council, which supports a merger with Bournemouth and Christchurch, said the upgrade was "much needed".
Dorset's nine councils are considering a major reorganisation that would leave just two unitary authorities in the county.
But the Conservative-led Borough of Poole said the civic centre had not been updated or refurbished since its opening 30 years ago.
Lib Dem councillor Mike Brook said: "They are wanting to spend on a building that they may not even have in between two and four years time and yet they are demanding cuts from the public, they are closing toilets, they are hiking up the car parking charges and just grabbing money and not really considering the long-term impacts of what they are doing."
Poole resident and campaigner Bob Lister said: "How can you spend £31,000 on furniture for a foyer? The costs are astronomical for what's required. It just needs a lick of paint and a slight update.
"There is already disabled access. It's just a waste of money on a building which is going to be closed in two to four years time."
A spokesman for Borough of Poole said the work would "improve the customer journey for all visitors".
A statement said: "Many people who use the customer inquiry centre are in a vulnerable position and this much-needed refurbishment will help to create a space that is comfortable and unintimidating, helping those in need achieve the best possible start to their process.
"More than half the cost for this proposal is drawn from existing budgets and all new facilities implemented will ensure that Borough of Poole finance reception is accessible for all users for the foreseeable future."
Poole's council is being criticised for spending £250,000 on revamping its civic centre which could close if a merger of Dorset councils goes ahead.