Sen. Sheldon Whitehouse told the Supreme Court that he intends to introduce legislation this year meant to shed light on the funding behind groups that frequently file briefs aimed at influencing the outcome of high-profile cases.

The Rhode Island Democrat often decries how high-dollar, dark money donations can be funneled through advocacy groups to anonymously press political agendas through the Supreme Court and lower appeals courts — what he dubs “judicial lobbying efforts.”

This month, Whitehouse sent draft legislation to Chief Justice John G. Roberts Jr. along with his concerns that the Supreme Court is not fairly enforcing a high court rule that prohibits someone from filing a brief known as an amicus curiae when contributors to the effort are anonymous.

The revelation Tuesday of the bill and a private Jan. 4 letter to Roberts and Scott Harris, the Supreme Court clerk, gives a rare glimpse into interactions between Congress and the high court on the legislative process. Whitehouse has not publicly spoken about his draft bill, a spokesman said.

These “friend of the court” briefs are a way for lawmakers, advocacy organizations, business groups, legal experts and others to speak directly to the justices and judges. The most high-profile cases generally attract the most amicus briefs, such as the legal fights over the 2010 health care overhaul or social issues such as same-sex marriage.

The Supreme Court last year rejected a brief from the U.S. Alcohol Policy Alliance because some of the group’s donors had contributed anonymously to the effort through the crowdfunding website GoFundMe. The group resubmitted the brief with a list of only donors who agreed to be named.

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But Whitehouse pointed out that the justices routinely accept briefs from special interest groups that frequently fail to disclose their donors, such as the U.S. Chamber of Commerce. The Chamber affirms to the justices that its “members” made a monetary contribution to the brief, but also “takes pains to conceal the identity of its membership,” the senator wrote.

Whitehouse, a Senate Judiciary member, told Roberts that if the Supreme Court interprets its disclosure rule to prohibit “contributions by only small-dollar donors and not wealthy and corporate interests,” then it is failing to meet the objective of making public who is behind efforts to influence the court.

“That the Court allows this type of concealment by the Chamber as a matter of course, while forcing anonymous $25 donors to return their contributions, is a perverse result indeed,” he wrote to Roberts.

Whitehouse also wrote that one group, the Lynde and Harry Bradley Foundation, bankrolled not only the nonprofit law firm that brought a case about union fees last term, but also donated to 11 different organizations that filed amicus briefs that supported the effort. And, he said, none of those groups disclosed the Bradley Foundation as the source of their funding.

Whitehouse first told the court about his concern in that case in an amicus brief he filed with Connecticut Democratic Sen. Richard Blumenthal. In a 5-4 opinion, the court overturned a decades-old precedent that allowed unions to collect fees from teachers and other public sector employees who were not in the union.

The Rhode Island senator wrote that he believes “a legislative solution may be in order to put all amicus funders on an equal playing field.” The bill, as written, would require the disclosure of contributions to any person or their affiliates that files three or more amicus briefs in a year at the Supreme Court and federal appeals courts.

Whitehouse wrote that he intends to introduce the “Assessing Monetary Influence in the Courts of the United States Act of 2019,” and asked for the chief justice’s feedback and information about the court’s disclosure rule. The bill likely faces strong political headwinds from Senate Republicans.

The draft also proposes to prohibit anyone covered under the bill from making a gift or providing travel to an appeals court judge or Supreme Court justice.

Whitehouse filed the letter to Roberts in a federal appeals court in California as part of his own amicus brief in an environmental lawsuit, in which he contests how the Chamber described its approach to global climate change policies.

The Supreme Court’s Rule 37.6 states that amicus briefs must “identify every person other than the amicus curiae, its members, or its counsel, who made such a monetary contribution.”