An Illinois Democratic senator under federal investigation for fraud and bribery resigned Wednesday from his office after FBI agents raided his Chicago home and Springfield office earlier this year.

In a letter to the Secretary of the Senate, State Sen. Martin Sandoval said his resignation would be effective Jan. 1.

"it is with a heavy heart, I, Martin A. Sandoval, do hereby resign the office of state senator," he wrote.

CHICAGO POLICE HAVE SEIZED MORE THAN 10,000 GUNS IN 2019 - ONE EVERY 48 MINUTES

On Sept. 24, FBI agents raided Sandoval's offices and home looking for information on concrete and construction businesses as well as information related to bribery or theft of federal funds. They were also looking for information on a power company, officials, lobbyists, gambling interests, a red-light camera company and information on at least three suburban mayors.

Following the raid in his Chicago and Springfield offices, agents were also dispatched to his Cicero office.

The raid was also followed by federal law enforcement actions in the towns of McCook, Lyons and Summit -- all of which are part of Sandoval's district, according to reports from The Journal Gazzett & Times Courier and The Chicago Tribune.

The move comes after two months of pressure by Democratic Gov. J.B. Pritzker and other state leaders who demanded Sandoval step down as chairman of the Transportation Committee. Pritzker expressed concern about the state's $41.5 billion construction program, in which Sandoval had a leading role last spring.

Local news outlets previously reported federal agents also went to Bluff City Materials, a Bartlett sand and gravel operation owned by a major Sandoval donor and that his connections to Commonwealth Edison, where his daughter, Angie, has worked as a senior representative for years.

Sandoval has represented the 11th District since 2003.

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In his resignation letter, Sandoval said he continues to have respect for his constituents and that Illinois senators convinced him that his resignation was necessary for the party to move forward.

Calls to his office for comment by Fox News were not immediately returned.