SYDNEY — Political donations by mining companies preceded legislative approval for several Australian mining operations, including plans to develop the country’s biggest coal mine, according to a report by an independent Australian policy institute released on Thursday.

The report, by the , examined six cases where mining companies made donations to ’s major political parties and received favorable legislation for mining projects in the state of Queensland.

The report contends that the donations from the mining industry bought access to Queensland state officials, giving the industry an “undue influence on our democratic processes” and resulting in decisions that “have poor outcomes for our environment, economy and our communities.”

“Taking money from mining companies undermines the integrity of political decision-making,” Mark Ogge, the report’s co-author said in an interview. “It should be illegal. It is a conflict of interest.”

The report, written with the Australian Conservation Foundation, was released two days before Australia’s national elections, which are Saturday. While the timing appears intended to highlight the influence of the mining industry in politics — Australia’s campaign finance laws do not require disclosure of donations to major parties until months after the fact — the report does not refer to any contributions in the current election.

The report’s primary focus is on the Liberal National Party, led by Campbell Newman, which governed Queensland from 2012 to 2015, and his successor, Annastacia Palaszczuk, of the Labor Party, who took office there in 2015.

Queensland is home to several large and contentious mining projects, including in the Galilee Basin in central Queensland. Two new mines there could add an additional 120 million tons a year to Australia’s thermal coal exports.

One of the mines would be Australia’s largest and, environmentalists say, will damage the Great Barrier Reef.

The project’s developer, the Adani Group, a conglomerate based in India, donated $52,139 to the Queensland Liberal National Party and to the federal Liberal Party of Australia, from 2012 to 2015, the report said.

The report said Adani officials met with Anthony Lynham, the state’s minister for natural resources and mines, at least seven times and had 12 other meetings with state ministers in 2013 and 2014.

In late 2014, the government of Queensland agreed to invest up to $220 million in rail and port projects to support the new mine. It also changed the legislation to remove the right of the community to object to mining projects, the report said.

The Adani project was approved by Ms. Palaszczuk’s government, and included a plan approved by the federal environment minister, Greg Hunt, a Liberal Party member, to allow bigger coal ships to dock at the port of Abbot Point within the Great Barrier Reef on Queensland’s northeast coast. The plan called for the dredging of the port to accommodate larger ships, with the spoils dumped near the reef.

After an outcry from scientists and legal action by conservationists, the dredging decision was reversed. The dredge spoils will now be dumped on land.

But the report said Adani’s donations had “influenced the approval process, encouraging successive governments to ignore concerns regarding their suitability to operate.”

Ms. Palaszczuk defended her government’s actions, saying it had lowered the reporting requirement for political donations to $738 from $9,458, making government more transparent. And in a written statement, a spokesman for the Queensland government said it had restored laws to allow communities to weigh in on proposed mining projects.

The spokesman said the approval process for mining projects was extensive and transparent. It includes public consultation, environmental impact studies and strict conditions to protect the environment. Mine lease applications must also meet public interest requirements.

The mines minister for Queensland, Anthony Lynham, was on vacation and was not available for comment. Adnani officials did not respond to a request for comment.

The Adani case was just one example cited in the report.

Two oil companies, Beach Energy and Linc Energy, and the mining companies Karreman Quarries and New Hope Coal also made donations, according to the report, which says the companies received favorable treatment in return. Another company, Sibelco, spent money campaigning to support its sand mining operations ahead of the state election.

A spokeswoman for Sibelco, Helen Stanley, said the company had made no direct donations to political parties but had funded an electorate campaign in support of its sand mining operations on North Stradbroke Island. She said the campaign was run in 2013. In 2015, the Palaszczuk government said it would end sand mining on the island by 2019.

Beach Energy, Karreman Quarries and New Hope Coal did not respond to questions. Linc Energy is in receivership, a company spokeswoman said, adding she could not answer questions about the company’s political donations policy.

Over all, the report said, the Queensland Liberal National Party received more than $700,000 in donations from mining companies from 2011 to 2015. The mining industry also donated nearly $2.2 million to the federal Liberal Party of Australia, which now leads the national government, in the five years since July 2011. The Queensland Liberal National Party and the Liberal Party of Australia are not one and the same.

The Queensland Labor Party received $68,000 and the federal Labor party received $890,000 from donors connected to the mining industry over the same period.

A spokesman for the Liberal Party said in a written reply on Wednesday that he would not comment on a report he had not read, but pointed out that the Australia Institute, a research center, employed former Greens Party supporters in important roles.

Large mining projects often require state and federal government approval, especially if threatened species and their habitats are placed under duress by the proposed operation.

“The report demonstrates that money doesn’t just buy access, it buys outcomes,” said Lindy Edwards, a political scientist from the University of New South Wales. She said state laws around political donations should be overhauled, “at the federal level, the secrecy is so bad it is almost impossible to uncover corruption.”

Donations to any political party higher than $9,774 must be declared on the Australian Electoral Commission’s public register. But those declarations are made months after the money changes hands. Funds donated to the federal Liberal coalition, Labor party or Greens party leading up to national elections on Saturday will not be made public until February 2017.

Also, it can be difficult to track how much money and when a donor made a contribution.

The report cited the meetings that mining company executives had with senior politicians based on minutes from ministers’ diaries, which are publicly available.

“A farmer whose ground water is about to be drawn down or whose land is about to be polluted rarely has the money to secure that sort of access,” Mr. Ogge said.

Ms. Edwards said many factors determined whether a mine gained approval. “Royalties from the mine to the state government, jobs, the state’s economic welfare are all factors,” she said. “But there is an issue around ensuring that everyone’s voice is heard. Mining companies should not get better access to government decision makers than people in the community, who are concerned about the environment.”