A wealthy fundraising body linked to the Liberal Party has quietly begun bankrolling the organisations behind two of the Coalition's biggest crossbench supporters in the finely balanced Senate.

The Cormack Foundation has donated more than $40 million to the Liberal Party over the last 18 years – including more than $3 million in 2015-16 – making it one of the party's biggest benefactors.

The foundation is an investment company and "associated entity" of the Liberals that donates dividends from its share portfolio. It has stakes in a number of blue-chip companies – including the big four banks, Rio Tinto, BHP Billiton, Telstra and Wesfarmers – raising about $3.9 million last year.

But for the first time in its 30-year history, the foundation last year donated to parties other than the Liberals – giving $25,000 each to the conservative Family First and the libertarian Liberal Democrats, according to the Australian Election Commission annual returns released this week.