Sen. Mitt Romney was caught drinking chocolate milk out of a bottle on the Senate floor on Tuesday afternoon — a breach of the Senate impeachment trial rules.

Under rules imposed during President Donald Trump's impeachment trial, senators are only allowed to drink water or milk out of a glass, and they're barred from using iPhones, talking, or standing.

At least four other senators have been spotted drinking milk in the Senate chamber during the impeachment trial.

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Sen. Mitt Romney, a Utah Republican, was caught drinking chocolate milk out of a bottle on the Senate floor on Tuesday afternoon — a breach of the Senate impeachment trial rules.

Under those rules, senators are only allowed to drink milk and water, and the beverages must be consumed out of a glass.

A Senate aide informed Romney that he was in violation of the rules and the senator left the chamber with the bottle, returning with the chocolate milk in a glass, The Wall Street Journal reported. The glass was inspected and Romney was allowed to enter with it.

Romney has been known to enjoy chocolate milk. His wife, Ann Romney, revealed that the drink is his "guilty pleasure" in a 2012 interview, and the then-presidential candidate was photographed sipping chocolate milk on his campaign bus.

Normal Senate rules prohibit food and drink on the floor, but the body has imposed additional rules for President Donald Trump's impeachment trial, including barring iPhones and prohibiting talking or standing. Water is served to lawmakers by pages, who give them the option of still or sparkling.

Milk is allowed via a precedent that dates back to 1966. Riddick's Senate Procedure states: "Senate rules do not prohibit a Senator from sipping milk during his speech." Though food is not allowed on the Senate floor, an exception has long been granted to the so-called "candy desk."

At least four other senators — Wisconsin Democrat Tammy Baldwin, Arkansas Republican Tom Cotton, North Carolina Republican Richard Burr, and Texas Republican Ted Cruz — have been spotted drinking milk in the Senate chamber during the impeachment trial.

Romney is a key player in the impeachment trial as he's expressed willingness to defect from his party and vote in favor of calling witnesses to testify.

John Haltiwanger contributed to this story.