International institutions play a key role in sanctions success. However, little is known about when senders mobilize institutional sanctions and how they induce international institutions to support their sanctioning efforts. Senders may need institutional support when they expect third-party states to engage in sanctions-busting. I suggest that senders anticipate sanctions-busting when they face third-party rivals which also have an alliance tie with targets. The presence of such potential sanctions busters may lead senders to seek institutional support. Also, senders should possess substantial material power to induce member states of international institutions to approve the sanctioning efforts. I assess the theoretical claim of this research by analyzing 1,038 sanctions episodes over the period 1951–2005. The findings support my argument that senders pursue institutional support when they face potential sanctions busters, and the success of their efforts partly depend on their material power.