The ability of cellular membranes to generate electrically-induced mechanical force (EMF) has been demonstrated in many cell types, including cochlear outer hair cells, axons, and some cultured mammalian cells. Models of membrane based EMF generation are based on an interaction between the transmembrane electric field and membrane surface charge. We use a technique that combines optical trapping with voltage clamping to investigate the effects of an electrically charged amphipathic agent on EMF by membrane tethers. Our preliminary results indicate that salicylate, a negatively charged amphipathic agent, which is also known to cause reversible hearing loss and reduce outer hair cell electromotility, reduces EMF in membrane tethers. These measurements provide a basis to better understand the role of membrane charge properties in EMF generation.