WASHINGTON -- In a looming vote that already has stirred passions on California campuses, a labor union representing graduate students in the state university system will decide this week whether to formally endorse a boycott of Israel.

The University of California Student-Workers Union, a local union of the United Auto Workers covering 12,000 teaching assistants, tutors and other students, will vote Thursday on a ballot initiative in support of the Boycott, Divestment and Sanctions Movement, the pro-Palestinian campaign that calls for a boycott of Israel. The ballot text proposes supporting the boycott until Israel "has complied with international law and respected the rights of Palestinians."

In the event of an aye vote, the union will call on both the University of California system and the UAW international union to divest from companies that the pro-BDS caucus deems "complicit in Israeli occupation of Palestine and its apartheid policies." The initiative also invites graduate students to take a personal vow declining participation in research or conferences sponsored by Israeli schools that BDS backers consider similarly accountable.

As with nearly anything touching on the Israeli-Palestinian conflict, the union's boycott vote presents some thorny politics. For one, the measure effectively would call for a boycott of companies that employ other UAW workers, such as Lockheed Martin. The California Teamsters, which also represent workers at companies that fall under the boycott, havecalled the BDS measure "hostile" and said they would "find it difficult" to defend the union in solidarity in the future.

The UAW, which narrowly lost a union vote at a Volkswagen plant in Tennessee that drew national attention earlier this year, doesn't appear eager to wade into such a feverish debate, though Thursday's vote may force it to. A union spokeswoman didn't respond to repeated requests for comment from HuffPost.

Last week, however, one of the international union's regional directors sent a letter to the local, reiterating the union's earlier opposition to a boycott of Israel. Organized labor in the U.S. has supported the Jewish Labor Committee in its condemnation of a boycott. Unions overseas, such as the Teachers' Union of Ireland, have proven more willing to do so. (The Chicago-based Industrial Workers of the World, a union with radical roots that remains well to the left of mainstream U.S. organized labor, endorsed BDS in 2010.)

The BDS ballot measure enjoys the majority support of the UAW local union's joint council, a body of elected officers from nine California campuses. The council agreed this summer to put the measure on the ballot for a union-wide vote.

But a group called "Informed Grads" has launched a counter campaign aimed at defeating the BDS initiative, which it says will "hurt our union, stifle academic freedom, and hinder peace." Members of the group describe the ballot measure as divisive and distracting.

"Most of the students I speak to are just astounded that our union would endorse an academic boycott," said Josh Saidoff, a graduate student in political science at UCLA. "It's in direct contradiction of freedom of expression and a free exchange of ideas."

Saidoff said the initiative came as "very much a surprise" when it was announced, and he accused the union council of being dismissive of critics' concerns.

Erik Green, financial secretary for the local and a graduate student at the University of California at Santa Cruz, said that the union has tried to "make sure all voices have a chance to express their views."

"We had pretty significant grassroots organizing in support of this. That's why it was brought up to the joint council," said Green. "We want the membership to be the one to make the decision."

The BDS movement notched a victory last year when two academic groups -- the American Studies Association and the Association for Asian American Studies -- threw their support behind the boycott. The move by the ASA, which represents college professors, sparked a heated debate and drew criticism that it was undermining academic freedom. (A larger professors' group, the American Association of University Professors, said it opposed the boycott.)

Alborz Ghandehari, a graduate student at University of California at San Diego and a member of the pro-BDS caucus in the union, said he viewed the vote as a show of support for Palestinian unions.

"We felt in our role as students and workers that we should respond to this call for solidarity from our Palestinian counterparts," he said.

But Karra Greenberg, a doctoral student in sociology at UCLA, said a vote in favor of BDS would undermine the union's own solidarity with other UAW locals in which members are employed by companies under the boycott. In her view, the union has more pressing parochial issues to address than conflict in the Middle East. She pointed to the prospect of a UC tuition increase now being debated by California lawmakers.

"Their focus is on BDS, and there are way more serious things we need our union membership focusing on," Greenberg said. "That just doesn't appear to be the case right now."