German Chancellor Angela Merkel's center-left rival in next year's election issued a bold challenge Tuesday to her government — going well beyond legal requirements to state that he earned €1.25 million ($1.6 million) over three years giving lectures.

The move by Peer Steinbrueck, Germany's finance minister from 2005-09, was designed to deflect any criticism of him for taking money from financial institutions for speeches and to press for more detailed earnings statements from all German lawmakers.

"I want to set an example that other parties in Parliament should follow," Steinbrueck said Tuesday, predicting that attacks on him would "boomerang."

The main opposition Social Democrats a month ago nominated Steinbrueck as Merkel's challenger in an election expected next September.

Opponents then drew attention to his earnings as a paid speaker after leaving his ministerial post, at a time when he was still a lawmaker. Steinbrueck and his party plan to make combating perceived financial-sector excesses a central election issue, and some in Merkel's center-right coalition suggested he risked appearing too close to the financial industry.

Steinbrueck struck back by commissioning a full audit of his earnings, going beyond German Parliament rules that require lawmakers to disclose outside earnings only in very general terms.

In the audit, Steinbrueck detailed 89 lectures to events organized by banks and other companies for which he was paid as much as €25,000 ($32,250). He said that income was taxed at Germany's top rate of 48 percent. He also made more than 200 speeches to universities and other institutions without taking a fee.

Steinbrueck, who has been widely praised for helping steer Germany safely through the 2008 financial crisis, said he used the lectures to "read the riot act" to bankers. He said it was "absurd and more than that" to suggest that giving paid lectures made him dependent on the financial industry. He said it's also his job to reach out to people who aren't natural Social Democratic voters.

Steinbrueck's Social Democrats and their allies, the Greens, have used the flap to push for far stricter earnings disclosure rules for lawmakers. Merkel's coalition has proposed tightening the system somewhat, but not as much as the opposition have demanded.

German lawmakers are paid €7,668 ($9,900) per month. Steinbrueck said he doesn't receive that salary, however, because he receives payments as a former member of a state government instead.