A top Democratic donation processor, Act Blue, is facing an investigation over concerns that the donation processing service is being used to circumvent campaign finance laws.

The Republican-led House Oversight Committee launched the investigation, citing “reports of potentially fraudulent and illicit financial activity” in a letter to Treasury Secretary Janet Yellen. 

The lawmakers ask Yellen for copies of financial suspicious activity reports related to ActBlue, which serves as an online catch-all processor for online donations to Democratic candidates.