SUGAR GROVE, Ill. (AP) — Defeated Republican congressional candidate Jim Oberweis announced Monday he has informed the U.S. House of Representatives he will contest the outcome of his race against Democratic Congresswoman Lauren Underwood.

In announcing his plans, Oberweis said during the discovery recount process, volunteers for his campaign found election jurisdictions around the 14th Congressional District did not follow the law. He claims that led to an inability to verify those who were legally entitled to vote actually voted.

Oberweis pointed to the lack of initials on vote-by-bail ballots in Kane County and a person from Kenosha, Wisconsin voting illegally to back his effort.

“Based on the findings in the discovery recount our campaign provided Congress we believe that there is sufficient evidence to show that I won the election for Congress in the 14th District in November,” Oberweis said.

The race between Oberweis and Underwood was among the most expensive in Illinois. Underwood raised more than $7 million, while Oberweis raised about $2.5 million.

The largely white district outside Chicago has historically been Republican but flipped in 2018. Underwood, who is Black, was the first woman and first minority to win the congressional seat once held by Speaker Dennis Hastert. She ousted four-term Republican Randy Hultgren in a Democratic wave.