Las Vegas Sands chairman and CEO Sheldon Adelson, and his wife Miriam, gave the National Republican Congressional Committee $25 million last month, according to federal filings.
The couple already gave $30 million to the same group, which provides financial support for Republicans running for office.
According to Bloomberg, the donation went to the Senate Leadership Fund.
The donation is part of the effort by both parties to build up campaign war chests ahead of November's midterm elections. Bloomberg reports the Democratic Congressional Campaign Committee has outraised the Republican Congressional Campaign Committee.