Sen. Josh Hawley, R-Mo., is demanding answers from Major League Baseball after the league warned three San Francisco Giants pitchers who wrote Bible verse references on their caps during a Pride Night game.

San Francisco starter Landen Roupp and two other pitchers added Bible verses to their Pride Night caps last week.

Roupp started the 5-1 loss to the Chicago Cubs last Friday night with "Gen 9:12-16" written on his cap. San Francisco relievers JT Brubaker and Ryan Walker also added Bible verses to their caps.

MLB issued a warning about future violations of the league's uniform policy.

"The writing on the cap violates our rules and consistent with normal practice we have warned the players about future violations," MLB said in its original statement.

The league issued another statement Tuesday to elaborate.

"To be clear, this routine verbal warning not to wear the hat in future games is not disciplinary and had absolutely nothing to do with the content of the message," MLB said.

"We respect players' right to free expression. However, writing of any kind, with any message, is prohibited per Major League Baseball's Uniform Regulations which provides in part that, '(a) Player may not write, attach, affix, embroider or otherwise display nicknames or messages on apparel or playing equipment…'. We have given the same warning numerous times in the past to players for messages such as 'Dad', 'Happy Mother's Day, I Love Mom,' and names of family members."

In a letter to Commissioner Rob Manfred, Hawley challenged MLB's explanation.

"MLB has said this is a content-neutral policy and that MLB 'respect[s] players' right to free expression.' But this is dubious, given that MLB is openly promoting a political viewpoint and possibly compelling adherence to that viewpoint," Hawley wrote.

Hawley argued the league's explanation is inconsistent with its past actions.

"The league's claim that it merely forbids 'writing of any kind' on its uniforms does not survive a cursory review of the league's recent history," Hawley wrote.

He pointed to MLB's support for messages such as "Black Lives Matter" and "United for Change" during the 2020 season, arguing the league previously permitted political and social messaging on uniforms, equipment, and fields.

MLB permitted players to wear league-approved patches bearing messages such as "Black Lives Matter" and "United for Change" during the 2020 season.

"Yet when three players added a handful of characters citing the Book of Genesis to their caps, the league reached for its rulebook," Hawley wrote.

He also cited a recent undercover investigation involving the Washington Nationals.

"This follows a high-profile undercover investigation that revealed at least one MLB team discriminated against a player based on his Catholic faith," Hawley wrote.

"You must answer for what appears to be a pattern of discrimination within MLB against baseball players who profess their Christian faith."

Hawley requested documents related to the uniform policy, past enforcement actions, any guidance involving Pride Night apparel, and records concerning MLB's approval of previous social or political messages.

He also asked MLB to provide records showing every instance during the past five seasons in which players were warned, fined, or otherwise disciplined under the uniform rule, along with the messages involved and the action taken by the league.

"The freedom to live out one's faith does not end at the ballpark gate," Hawley wrote.

"Americans of every creed are entitled to confidence that the institutions of our national pastime will not single out religious expression for punishment while celebrating messages of the league's own choosing."

He requested a response from MLB by June 19.

The Associated Press contributed to this report.