If the Economy is bad, don't strike because times are bad.
If the Economy is good, don't strike because times are good.
If the Economy is average, don't strike because there's never a good time to strike.
Let's face it, some people will never vote to strike, no matter what the issues. Period.
They probably believe "No one wins in a strike." When, in fact, the Union does win, if you include all the bad language kept out of a proposed Contract, as well as any actual gains made.
Or they believe they will be fired, or replaced by "replacement workers." When, In fact, no one can be fired during a strike, unless you otherwise do something illegal.
In an Unfair Labor Practice (ULP) strike, which this situation would be, any replacement workers must be themselves fired when the strike is over, and all strikers go back to work. That fact alone usually makes it hard to even find people to hire, and then train, for such a short time.
Usually just the threat of a ULP strike is enough to tell the Company we are serious. Giving a 72-hour strike notice may well get results without a strike being necessary. UPS would not want the PR disaster that comes when workers who make $8.50 per hour (about minimum wage) and up, are striking on principle to enforce the mutually agreed-to Contract, and mutually agreed-to national panel decisions, and not for money.
I think you should strike anytime your rights are being violated in a big way, and all other avenues of redress have proven fruitless. Otherwise you're admitting the Contract is just a bunch of unenforceable suggestions, and you don't much care what the Company does to you and your fellow workers.