Sen. Chuck GrassleyCharles (Chuck) Ernest GrassleyFBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Klobuchar taking over Franken's sexual assault bill Lawyer: Kushner is 'the hero' in campaign emails regarding Russia MORE (R-Iowa) will vote against the Supreme Court confirmation of Judge Sonia Sotomayor when the matter comes to a vote on Tuesday.

The Des Moines Register reported on Monday that Grassley believes the federal appeals court judge would engage in judicial activism while serving on the bench. The fifth-term senator expressed similar concerns about Justice David Souter, whom Sotomayor will replace on the Court should she be confirmed.

"And consequently, I don't want someone succeeding him who doesn't have a clear role of what the Supreme Court is," Grassley told the Register.

The Iowa Republican was previously thought to be a "swing vote," so to speak, on Sotomayor's confirmation vote.

Grassley joins Republican Senate Judiciary Committee members John CornynJohn CornynGOP senator: ObamaCare fix could be in funding bill Senate GOP running out of options to stop Moore Texas Republicans slam White House over disaster relief request MORE (Tex.), Orrin HatchOrrin Grant HatchProminent conservative passes on Utah Senate bid Republicans offer this impossible choice: Tax cuts or senior care Senate GOP running out of options to stop Moore MORE (Utah), Jeff SessionsJefferson (Jeff) Beauregard SessionsFederal judge rules Trump defunding sanctuary cities 'unconstitutional on its face' FBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Alabama election has GOP racing against the clock MORE (Ala.), and Jon Kyl (Ariz.) in opposing Sotomayor's confirmation. Grassley is the second-ranking member of the committee.

Grassley previously voted against Sotomayor for her appointment to the appellate court in 1998. But when asked about it May he did not seem to remember why.