Senate Judiciary Committee ranking member Chuck GrassleyCharles (Chuck) Ernest GrassleyGrassley: 'Good chance' Senate panel will consider bills to protect Mueller Overnight Finance: CBO to release limited analysis of ObamaCare repeal bill | DOJ investigates Equifax stock sales | House weighs tougher rules for banks dealing with North Korea GOP state lawmakers meet to plan possible constitutional convention MORE (R-Iowa), along with a bipartisan group of 16 other senators, called on Attorney General Eric HolderEric H. HolderJuan Williams: Momentum builds against gerrymandering GOP worries as state Dems outperform in special elections House votes to curb asset seizures MORE this week to conduct a "comprehensive and exhaustive investigation" into the "potentially illegal misappropriation of funds" from MF Global customers.

"If the Department's ongoing investigation uncovers illegal actions, criminal prosecution should be pursued without hesitation," the senators wrote to Holder on Wednesday. "In order to get to the bottom of this, we urge federal agents to use every legal resource available."

The letter added that the bankruptcy of MF Global is posing the risk that thousands of farmers and other Americans stand to lose money in their accounts, even though federal rules require collateral to be held in customer segregated accounts.

"If credible evidence of illegalities is found by the investigation, significant resources should be utilized to prosecute those responsible," the letter said.

The bankruptcy has revealed that MF Global might have made proprietary investments with the collateral of its customers. The bankruptcy was prompted by fears that MF Global held too much risky sovereign debt.

Democrats on the letter are Senate Finance Committee Chairman Max BaucusMax Sieben BaucusBernie Sanders flexes power on single-payer ObamaCare architect supports single-payer system Trump has yet to travel west as president MORE (Mont.) and Sens. Ben Nelson (Neb.), Kent Conrad (N.D.), Sherrod BrownSherrod Campbell Brown'Hillbilly Elegy' author won't run for Senate Brown, Portman urge Trump administration to move quickly on a steel decision Dems call on DeVos to work with CFPB to protect student borrowers MORE (Ohio) and Amy KlobucharAmy Jean KlobucharWeek ahead: Crunch time for defense bill’s cyber reforms | Equifax under scrutiny Some Dems sizzle, others see their stock fall on road to 2020 Consumers the big winners of Amazon-Whole Foods merger MORE (Minn.).