Anti-choice group Susan B. Anthony List (SBA List) is ramping up efforts to hold onto incumbent Republican Sen. Roy Blunt’s seat in Missouri. Polls show Blunt virtually tied with his Democratic challenger, Secretary of State Jason Kander.

A Monmouth University poll released Tuesday found Blunt and Kander neck and neck in their bid for the Senate, with the GOP incumbent leading by one point: 47 percent to Kander’s 46 percent. Though Blunt had been up by five points in August, his lead has dwindled.

The results of the race will likely help determine which party will hold the Senate.

SBA List on Monday announced a last-minute six-figure digital ad buy in Missouri and North Carolina, in an effort to reach 550,000 anti-choice “low propensity voters multiple times online.”

The anti-choice group announced in mid-October its plans to invest heavily in Missouri’s U.S. Senate race between Blunt and Kander, as well as in the state’s gubernatorial race. The group said it planned to spend $500,000 in the state and aimed “to make 250,000 voter contacts in Missouri over the next few weeks through mail, digital advertising, and knocking 25,000 doors,” according to a press release.

“The race in Missouri is critical to maintain our pro-life majority in the U.S. Senate, so we’re expanding our existing campaign to help Sen. Blunt,” the organization’s president, Marjorie Dannenfelser, said in a statement.

Marilyn Musgrave, vice president for government affairs at SBA List, in a Tuesday article for anti-choice site Life News called Missouri an anti-abortion “battleground we must win.” She pointed to Blunt’s consistent opposition to reproductive rights.

SBA List’s affiliated super PAC, Women Speak Out PAC, has spent $87,737 opposing Kander in independent expenditures, electioneering communication, and communication costs, according to the Center for Responsive Politics’ Open Secrets database.

A lawsuit filed last week on behalf of Missouri Democrats alleged that Blunt had coordinated with SBA List’s anti-choice PAC in what would be a breach of federal campaign regulations. The suit cited a CNN article reporting that “Blunt called SBA List President Marjorie Dannenfelser last week to raise more money, and the PAC for the conservative anti-abortion group is planning to spend $500,000 in the state on in-person, digital and mail outreach.”

Representatives from both SBA List and Blunt’s campaign have denied the accusations.

Blunt has been a consistent anti-choice voice in the Senate, and once attempted to push through the “Blunt Amendment,” legislation that sought to allow exemptions from the Affordable Care Act’s birth control benefit for employers or insurers who claimed to have moral objections to providing contraceptive coverage to employees.

He has co-sponsored other anti-choice legislation such as the medically and scientifically dubious “Pain-Capable Unborn Child Protection Act.”

Kander, in contrast, has been endorsed by reproductive rights groups NARAL Pro-Choice America and Planned Parenthood Action Fund. During his time in Missouri’s General Assembly, Kander voted against a ban on later abortion care.