Anti-gay protesters hold a sign outside San Antonio City Hall last month during a budget hearing where speakers focused largely on a proposal to offer domestic partner benefits.

The San Antonio City Council may be one vote short of the majority needed to approve a proposal to offer benefits to the domestic partners of employees, according to a source with knowledge of the situation.

The council is slated to vote on DP benefits as part of the city’s 2012 budget on Thursday morning. The DP benefits proposal, which would cost an estimated $300,000 per year, has met with vocal opposition from anti-gay religious leaders.

Both the Human Rights Campaign and Equality Texas have issued action alerts calling on San Antonio residents to contact their council members and urge them to support the proposal. Another LGBT group, the Direct Action Network of San Antonio, is asking people to wear purple to Thursday’s council meeting — as well as to another meeting Wednesday at City Hall — in a show of solidarity.

San Antonio is the nation’s seventh-largest city and would be the fifth in Texas to offer DP benefits to employees, joining Austin, Dallas, El Paso and Fort Worth.

An LGBT source with knowledge of the situation, who asked not to be identified, said this morning in an email that the 11-member council may be one vote short of the six votes needed to approve the proposal. The source also said DP benefits may be broken out of the budget and voted on separately.

“If this happens it will surely lose because it could hurt council members politically,” the source wrote.