A strike authorization vote always has to be held separately, this only give the union permission to call a strike if it comes to that. Voting down a contract does not and will not, in and of itself, declare a strike.
If you read the 2/3 rule in the IBT constitution, you will see that if the contract is turned down by a simple majority of more than 50% of eligible voters, or by 2/3 of less than 50% of eligible voters, a strike is automatically authorized.
Article 12 section 2
"all votes cast as follows:
(1) If at least one half of the members eligible to vote cast valid ballots then a cumulative majority of those voting in favor of the fnal offer shall result in acceptance of such offer; and a cumulative ma‑ jority of those voting against acceptance of the friend‑ nal offer
shall authorize a strike without any addi‑ tional vote being necessary for such strike authorization. A tie vote shall be resolved as pro‑ vided in Section 1(b)(l) of this Article�
(2) If less than half of the eligible members cast valid ballots, then a twothirds (2/3) vote of those voting shall be required to reject such fnal offer and
to authorize a strike. The failure of such membership to reject the fnal offer and to authorize a strike as herein provided shall require the negotiating com‑ mittee to accept such fnal offer or such additional provisions as can be negotiated by it"
Strike authorization votes can be called earlier in the process to give the union more leverage in negotiations. If a strike wasn't already authorized prior to the ratification vote, they would need the threat of a strike to get the company back to the table. Last contract, UPS stated publicly they were willing to continue negotiations, and even with a previously authorized strike, Teamsters ratified anyway.
