A battle is heating up at Kauffman Stadium but it's not about baseball, it's about abortion.

The pro-choice group, UltraViolet, wants the Kansas City Royals to end its marketing partnership with the pro-life organization, the Vitae Foundation.

Right now, the Royals run commercials for the Vitae group on the radio and at Kauffman Stadium.

On Tuesday, at Kauffman Stadium UltraViolet hired a messaging plane to fly over the stadium with the words, "ROYALS FANS DESERVE THE TRUTH — DROP VITAE".

Last week, UltraViolet launched a petition drive.

Its leaders said more than 40,000 people have signed the petition asking the Royals to end its relationship with the Vitae Foundation

"This partnership is part of a deceptive anti-choice agenda. The Kansas City Royals are not only condoning it but they are willingly participating edit and amplifying it," said Karin Roland, chief marketing officer for UltraViolet organization.

In one week, UltraViolet leaders told 41 Action News almost 45,000 people have signed the online petition asking the Royals to stop promoting Vitae.

Kansas City Royals TV Publicity Director Toby Cook last week responded to complaints from UltraViolet, with this statement:

"We entered into an agreement with the Vitae Foundation at the start of the 2016 season. It is primarily a radio advertisement buy. Vitae has similar agreements with other sports properties and media outlets. Separate from the ad campaign and as a general manner of practice, the Royals take no official position on culturally-sensitive issues."

A statement on Tuesday from Martha Schoenberg, Vitae Foundation Communications Director explained its mission.