The National Rifle Association is rebuffing a request from Sen. Ron Wyden (D-OR) for more details on whether it received Russian money aimed at influencing U.S. elections.

Two previous exchanges of letters between Wyden and the NRA revealed that the gun group accepts donations from foreign entities and moves money between its various accounts. But in a letter to Wyden sent Tuesday, the NRA said it had provided all the facts required to satisfy any “legitimate concerns.”

“Given the extraordinarily time-consuming and burdensome nature of your requests, we must respectfully decline to engage in this beyond the clear answers we have already provided,” NRA General Counsel John Frazer wrote in an April 10 letter.

Wyden’s office expressed its disappointment in a statement: “After three letters, the NRA continually, and specifically avoided detailing what measures it takes to vet donations, including from shell companies, a known means for Russians to funnel money into the United States.”

Wyden had asked for an in-depth account of how the group used the foreign donations made since 2015 and how it transfers funds between its accounts, among other queries. The FBI is reportedly probing whether the NRA received Russian money to boost Donald Trump’s 2016 campaign.

In the April 10 letter, the NRA said it received a total of $2,512.85 from Russians or U.S. citizens living in Russia between 2015 and the present. $525 of that came from contributions from two individuals, while the rest came from “about 23” other individuals for costs like membership dues and magazine subscriptions.

The NRA had previously only acknowledged receiving a donation from one Russian: Aleksandr Torshin, a Russian government banker with close ties to the gun group. The NRA has said it received under $1,000 from Torshin for his lifetime membership payment. In the latest letter, the group said it was “reviewing our responsibilities with respect to” Torshin after he was added to a list of Russians under U.S. sanction last week.

Treasury Department regulations “generally prohibit” U.S. persons from dealing with sanctioned individuals.

Wyden will refer his correspondence with the NRA to the Federal Elections Commission, an aide for the senator told TPM. The FEC has received a complaint from a liberal group to launch a full investigation into the NRA’s links with Russia, and is conducting a preliminary review of the facts.

Read the NRA’s full letter below.