Opponents of Measure B, a November ballot measure that would create a sales tax to fund a 16.1-mile extension of the Bay Area Rapid Transit (BART), are accusing the measure's supporters of working a bit too closely with the local transportation authority.

The group Citizens for Sensible Transportation: No on Measures B, C and D filed a complaint Thursday with the Fair Political Practices Commission (FPPC) charging the Silicon Valley Leadership Group, which supports Measure B, of failing to disclose in-kind donations from the Santa Clara Valley Transportation Authority.

The "No on B" group is using as the basis for its FPPC complaint the nearly 500 pages of e-mails between staffers from SVLG and the VTA that were released through a Public Records Act request. While most of these e-mails are little more than informational exchanges between staffers from the transportation authority and SVLG, several of them refer to meetings between officials from the two agencies to discuss media outreach strategies and campaign organizing.

The "No on B" campaign is using these documents as evidence that SVLG failed to report the authority's "significant donations of staff time and materials" to the pro-B campaign.

Specifically, the complaint refers to handouts, maps and graphics that VTA supplied to SVLG and to arranged meetings between staff members from the VTA and the SVLG.

Margaret Okuzumi, one of the leaders of the "No on B" campaign, said that while there's nothing wrong with the VTA providing information, the agency overstepped its boundaries when it created custom maps to meet SVLG's requests and collaborated with the leadership group on media outreach. The e-mails include exchanges in which spokespersons for the VTA and the SVLG discuss getting together to talk about strategies for reaching out to newspapers.

"It's clear the VTA has crossed the line from being an impartial agent and is actually engaging in advocacy," Okuzumi said. "At the very least, there needs to be more transparency in how the VTA has been invested in the 'Yes on B' campaign."

But Phil Yost, spokesman for the "Yes on B" campaign, dismissed the complaint as baseless and said the transportation authority was simply fulfilling its duty as a public agency by providing the requested materials.

"The opponents of Measure B understand how popular BART is among voters of this county and are raising smoke about issues that are non-issues," Yost said. "VTA is in charge of this project. It's the source of information on ridership, costs and routes and it provides that information to anyone because they're a public agency."

Jennie Loft, spokesperson for VTA, said the authority responds to all requests for information from the public, "regardless of their organizational or political affiliations"

"VTA provided information, as requested, fulfilling our responsibility to do so as a public agency," Loft said in an e-mailed response. "We make every effort to provide accurate, timely information, in a fair, open, and consistent manner."

She did not dispute any of the allegations.

The proposed measure would create a 1/8 cent sales tax to operate, maintain and improve a 16-mile extension of BART between San Jose and Fremont. The funds would only be collected if state or federal funds are acquired to match local spending.