Pressure is growing on the longest-serving state House speaker in American history to resign as federal investigators probe his relationships with corporate lobbyists.

The once-powerful state officeholder previously resigned as chairman of the influential Illinois Senate Transportation Committee in October.

State Sen. Martin Sandoval has resigned as chairman of the powerful Illinois Senate Transportation Committee, weeks after federal authorities raided Sandoval’s home and offices as part of an ongoing corruption probe.

The lawmaker who carried to the governor’s desk an infrastructure plan that doubled the state’s gas tax used his influence as a powerful state lawmaker to land his son a government job, a lawsuit alleges.