The San Diego Tourism Authority and the San Diego County Hotel-Motel Association have issued a joint statement opposing both November ballot measures that call for hikes in the city’s hotel taxes.

On Nov. 8, voters will decide the fate of Measure C, the San Diego Chargers’ proposal to fund a new $1.8 billion downtown “convadium” via a 4 percent hike in hotel taxes; and Measure D, a proposal by a citizens’ group led by attorney Cory Briggs that would raise taxes 3 percent to potentially fund projects including a non-waterfront convention facility and improvements to the current Mission Valley site of Qualcomm Stadium.

According to the city attorney, both measures will need two-thirds voter approval in order to pass.

In their statement, the tourism and hotel organizations warned against both measures’ proposed elimination of the San Diego Tourism Marketing District, which has been “a proven source of revenue” for marketing San Diego as a visitor destination.

The groups said both C and D would also prohibit expansion of the current convention center, needed to retain big gatherings like Comic-Con International; raise taxes to a level where San Diego would be at a competitive disadvantage; and could negatively impact the city’s general fund due to “unreliable” forecasts for revenue and expenses.

Similar objections were previously raised about the Chargers’ plan by the executive boards of the tourism authority, the San Diego Convention Center Corp., and the hotelier-led tourism marketing district.

The nonprofit San Diego Tourism Authority, established in 1954, includes 996 member organizations and gets the majority of its funding from the San Diego Tourism Marketing District, which collects a 2 percent assessment from local hotels to support tourism promotion.

San Diego County Hotel-Motel Association is a federation of property owners and operators, representing hotels with a total of approximately 22,000 rooms countywide.