Billionaire Clive Palmer was Australia's biggest political donor last year, giving a whopping $5.9 million to himself.

Unions also flexed their muscles in Queensland with a combined $1.056 million pumped into the Queensland Labor Party's war chest, while businessman Anthony Pratt's Pratt Holdings gave $1.55 million, mostly to the Liberal party but also $250,000 to the Nationals.

The donations were revealed in the political party annual returns for 2019-20 published by the Australian Electoral Commission on Monday.

The Bob Brown Foundation, behind the infamous anti-Adani convoy just prior to this disclosed period, received $415,000 in donations and declared $213,000 on electoral expenditure.

Labor's left-faction aligned United Workers Union, formerly United Voice, was the most generous giving $328,832, while the CEPU and conservative SDA union each handed over about $200,000.

While the CFMEU in Queensland threatened in August to pull funding and volunteers from Labor, the construction union still made $134,895 in donations to the party in the 2019-20 financial year. The Transport Workers Union and AWU also chipped in.

The LNP's Queensland donors included Suez Recycling which gave $77,000, Macquarie Telecom with $58,500 and Boyce Pastoral Company handed over $45,796.

The biggest donors in the country include businessman Anthony Pratt's Pratt Holdings, while gas company Woodside Energy gave $335,000 in a mix to both Liberal and Labor.

The Pharmacy Guild of Australia was also one of the top donors, splashing out $214,000 in 2019-20 to both major parties, while Pfizer Australia gave $47,140.

Left-leaning political outfit GetUp! declared it received $10 million in receipts, while conservative lobby group Advance Australia showed it received just $1.3 million.

But Mr Palmer's United Australia Party, which received less than 0.3 per cent of the vote for the Senate in Queensland, declared receipts of $10.18 million.

The largest single donation in the country in 2019-20 came from Mr Palmer's own company Mineralogy which gave $5.9 million.

Pauline Hanson's One Nation declared $5.78 million in receipts, mostly from the Australian Electoral Commission and the party's state branches.

The Queensland Greens received $2.8 million in payments, with the largest single donation coming from mathematician and professional gambler Duncan Turpie who gave $100,000.

The minimum threshold for donation declaration is $14,000.

Originally published as Unions pump $1m into Qld Labor's war chest