Disputes that work start with documents
You will rarely win an argument about whether the work is needed without seeing the engineer's report, the bids and the reserve study. Owners generally have a legal right to inspect and copy these. Ask in writing and keep proof you sent it.
What to look for
How it was approved: was a vote needed, and was the meeting properly noticed?
What it pays for: required repairs, or upgrades mixed in?
How your share was worked out: does it match the percentage in your declaration?
Whether insurance should be paying for part of it.
Whether the reserve study warned about this years ago and the board under-funded it. That doesn't cancel the bill, but it is useful at the next election.
How to raise it
Put your questions in writing to the board, ask for them to go in the minutes, and attend the meeting. Talk to your neighbours; a group of owners asking the same questions gets answers faster. If the documents show a real legal problem, a lawyer licensed in your state can tell you whether it's worth challenging.
General information, not legal advice. Rules vary by state and by your governing documents.