Nope, they didn't. The Sierra Club never, ever supported immigration restriction; the one time it came up on the ballot, it was voted down by a ratio of 3:2. (By, yes, the Club members in an election, not the Board of Directors.) Election results here.
I assume that any result that close was probably susceptible to being determined by who controlled the wording of the ballot question and the use of official resources in campaigning.
Apparently A was put on the ballot by gathering signatures, and then B was put on with wording designed to counter to it. Apparently the organization's leadership largely supported B. Those are great advantages for B, and it didn't even get more than 3/5 of the popular vote.
Who could vote for A instead of B, when B is a vote for "the empowerment and equity of women"...
A response essay written by Eliezer Yudkowsky posted at Cato Unbound for the issue Brain, Belief, and Politics:
Is That Your True Rejection? by Eliezer Yudkowsky
The lead essay has been written by Michael Shermer:
Liberty and Science by Michael Shermer