Sens. Sheldon Whitehouse (D-R.I.) and John Kennedy (R-La.) in a bipartisan effort asked the Department of Justice (DOJ) and the U.S. Marshals Service for Supreme Court travel records in a probe. 

In a letter to the DOJ and Marshals Service on Friday, both senators asked for access to the trips the Supreme Court justices took in the last 10 years. 

They asked for documents for trips outside of Washington, D.C., the names of judges who took those trips, the cities and airports the judges traveled to and the cost of U.S. marshals to accompany them for each trip. 

Supreme Court justices can request additional security from the U.S. Marshals Service for domestic travel, according to a Roll Call report on Tuesday.

Whitehouse and Kennedy cited the Ethics Reform Act of 1989 and the Ethics in Government Act of 1978 as a reason why they are taking this approach, which requires Senior government officials to disclose outside income, gifts and reimbursements on an annual basis.

Both lawmakers added that justices' guidelines compared to other lawmakers are "significantly less stringent". 

"The Judicial Branch’s comparable guidelines are significantly less stringent. Even those requirements, however, do not formally apply to the justices of the Supreme Court. As a result, the justices of our highest court are subject to the lowest standards of transparency of any senior officials across the federal government," Whitehouse and Kennedy said in their letter.