The fundraiser is part of an ongoing effort from Bloomberg to thank vulnerable senators who fought for gun control measures.
His group, Mayors Against Illegal Guns, has run ads thanking Sen. Pat Toomey (R-Pa.) for his work on a bipartisan measure, along with Manchin, to expand background checks.
Tickets for the Manchin fundraiser range from $1,000 to $5,000. The Mountain State senator isn't up for reelection until 2016, but he's already become a target of gun-rights groups — and the issue will likely continue to dog him in his red-leaning state.
Bloomberg has also sought punitive responses to a number of "no" votes that gun-control advocates see as persuadable, including Sens. Kelly AyotteKelly AyotteGOP women push Trump on VP pick John Bolton PAC pours more cash into GOP campaigns Dem campaign arm: Poll numbers slipping for vulnerable Republicans MORE (R-N.H.), Jeff FlakeJeff FlakeMany Republicans uninterested in being Trump’s VP: report Senate confirms Obama's long-stalled ambassador to Mexico McCain fundraiser faces felony drug charges in Arizona MORE (R-Ariz.) and Mark PryorMark PryorEx-Sen. Kay Hagan joins lobby firm Top Democrats are no advocates for DC statehood Ex-Sen. Landrieu joins law and lobby firm MORE (D-Ark.), against whom the group has run ads.