His letter came a day after Live Action President Lila Rose announced that Google had removed her organization's ads, including one promoting the abortion reversal pill.
Hawley wrote: "When I spoke with Mark Zuckerberg about a similar issue in September 2019, he acknowledged the danger of bias on the parts of content reviewers in this area, particularly where pro-life activist groups like Live Action are concerned."
"But if your company’s behavior is any indication, those concerns have gone unaddressed. Rather, your company appears to have taken a page out of the progressive left playbook and has started targeting pregnancy resource centers and pro-life activist organizations for disfavor."
The Missouri senator also alleged that Google blocked ads from Choose Life Marketing, a company in his home state that helps spread awareness about aid provided by pregnancy resource centers.
Addressed to Google CEO Sundar Pichai, the letter made several requests that seemed designed to uncover potential ideological bias.
One of the questions asked, "At what rate are ads produced by crisis pregnancy centers, pro-life advocacy organizations and firms that work with them, deemed ineligible for distribution on Google’s platform?"
The senator also asked what "contacts have Google executives or other leaders had with abortion advocacy organizations in the last month?"
Rose tweeted Tuesday that Google had blocked 18 of her ads. Both she and Hawley suggested Google hypocritically favored organizations like Planned Parenthood.
When asked about Rose's accusations, a Google spokesperson said it had restored a video posted by Live Action.
"We do not permit ads with unproven medical claims. Medical experts have raised serious concerns about abortion reversal pills. Beyond protecting users from medical harm, our policies do not distinguish between promoting pro-choice and pro-life messages," the Google spokesperson said. "Advertisers are allowed to offer either abortion or abortion-alternative services. When doing so, both must prominently disclose which type of service they offer so that users have full transparency and can make their own decisions.
"The Live Action video ad does not violate any of our policies and is allowed to run as an ad. We have corrected the label that temporarily blocked its ability to be promoted."
On Wednesday, Rose told FOX Business that Google had only restored one of the 18 ads.
"It's extreme and unprecedented bias in support of the abortion industry," Rose told Fox News in an interview Tuesday. "They are currently allowing promotions for abortion pills, which force miscarriage, which end pregnancies and kill children, and they refuse to allow an FDA-approved treatment to be promoted to the women who want it."
Google did not immediately respond to FOX Business' request for comment.
Abortion pill reversal is a controversial topic and will likely garner additional attention as Texas implements its ban on abortions after a heartbeat is detected. With a spate of state-level bans and pending restrictions on access, women are more likely to seek medication abortions.
Abortion pill reversals involve using progesterone to reverse mifepristone's effect on the pregnancy-related hormone.
Google had cited a brief from the American College of Gynecologists-Obstetricians (ACOG), which Rose has described as "pro-abortion." Its website claims reversal isn't supported by science. By contrast, the American Association of Pro-Life Gynecologists and Obstetricians (AAPLOG) supports reversals.
In 2019, the group said: "By giving a woman progesterone, the Mifeprex abortion can be stopped and the chances of the baby surviving increase from 25% (the survival rate without natural progesterone) to 68% (the average survival rate after giving natural progesterone). This is a significantly increased chance of the baby surviving the attempted chemical abortion after Mifeprex. For women who change their mind after starting a chemical abortion, the administration of progesterone can give her a real hope of saving her unborn child."
FOX Business' Tyler O'Neil contributed to this report.