A prominent East Bay developer and Pleasanton resident was arraigned Monday on federal allegations he made illegal campaign finance donations to current U.S. Rep. Eric Swalwell's congressional campaign in 2012 and 2013.

The indictment alleges that Tong, 72, used straw donors, or "conduit contributors," in order to give more money than one person is allowed to give to a political campaign, according to U.S. Attorney Brian J. Stretch and FBI special agent in charge John F. Bennett

Authorities allege that in both 2012 and 2013, Tong made over $10,000 of these straw donations to the authorized political committee supporting the campaign of a candidate for a federal elected office. Tong pleaded not guilty to the charges Monday.

Neither the committee nor the candidate are identified in the indictment, but Swalwell released a statement through his campaign committee Wednesday acknowledging his campaign was investigated by federal authorities in connection with the Tong probe and denying any wrongdoing by himself or campaign officials.

"I'm deeply disappointed by what's alleged in the grand jury's indictment. My campaign never would have accepted a single penny of these contributions had we known how they were being made," said Swalwell, a third-term Democrat whose district includes Pleasanton.

The congressman said his campaign "cooperated fully" with federal investigators and the Department of Justice "does not suspect any wrongdoing on the part of myself or anyone with my campaign, nor that anyone in my campaign knew of the scheme outlined in the indictment."

"I will not tolerate illicit contributions like these in my campaign or in our political process generally," added Swalwell, who said his campaign is working with authorities to tally the straw donations to in turn donate that sum to a local charity.

In the indictment, Tong is charged with one count of making contributions of more than $10,000 in the names of straw donors to the candidate in 2012. The limit set by the Federal Election Campaign Act for contributions from any one person that year was $5,000.

The second count charges Tong with making contributions exceeding $10,000 to the same candidate's campaign committee in others' names. The limit for that year was $5,200.

The donations occurred on either end of Swalwell's first election to Congress. He was a 31-year-old Dublin councilman when he successfully unseated incumbent and fellow Democrat Pete Stark in November 2012. Swalwell won re-election twice since.

This week, after an initial appearance and arraignment in federal court in Oakland, Tong was released on his own recognizance and required to surrender his passport. His next appearance is scheduled for Sept. 29, before U.S. District Judge Jon S. Tigar for a status conference.

The Special Prosecution and National Security Unit of the U.S. Attorney's Office is prosecuting this case and is the result of a year-long FBI investigation.

Tong was also the subject of recent case involving fraud.

In December 2015, he pleaded no contest to violating the U.S. Endangered Species Act by submitting fraudulent documents to the city of Dublin that falsely stated he had paid $3.2 million in mitigation efforts for grading a Dublin development in a way that harmed the habitat of the endangered California tiger salamander.

As part of his plea deal, Tong agreed to pay about $1 million to state, county and nonprofit wildlife agencies and preserve 107 acres of land in Contra Costa County.

He also reached a separate plea deal in Alameda County Superior Court for the Dublin documentation fraud case.

Editor's note: Information from the Bay City News Service was used in this report.