The New York Post uncovered Federal Election Commission (FEC) records on Saturday that showed Mr Hawley used $197 (£143) of campaign funds to buy food for his family at Universal Studios vendors, including Margaritaville and Lard Lad Donuts.
The expenditure, which was made as part of a lobbyist retreat to Orlando, Florida, in February 2020, included $8.83 (£6.43) at Seuss Popcorn, $15.63 (£11.38) at Lard Lad, $30.41 (£22.14) at Bumblebee Taco, and $80.04 (£58.28) at Margaritaville.
The money spent has put the senator under scrutiny, as US politicians are prohibited from using their campaign funds for personal expenses.
Ann Ravel, a former chairwoman of the FEC, told The Post that Mr Hawley’s spending in Orlando appeared “to not be a legal use of campaign funds”.
While Larry Sabato, director of the University of Virginia’s Centre for Politics, agreed with that assessment, saying that “it does warrant some scrutiny.”
Mr Hawley’s office told Insider that the senator did pay back the money spent on the trip, but not until 30 January 2021.
His office said that the trip, for Mr Hawley and fellow Missouri senator Roy Blunt’s leadership PACs, is “designed specifically for families to attend. Guests are encouraged to bring their children and Sen Blunt has been hosting it for a number of years.”
Campaign finance violations can be serious; former California representative Duncan Hunter, a Republican, resigned from his post in 2020, after pleading guilty to using more than $150,000 (£109,999) of campaign funds on personal expenses, including fast food and cinema tickets.
Mr Hunter, who also spent the funds on buying pet rabbits and on luxury hotels, was sentenced to 11 months in prison, but was pardoned by Donald Trump before his sentence began.
Mr Hawley, who was elected as a senator in Missouri in 2019, has faced controversy over the last month after he led efforts in Congress to block the certification of votes to confirm Joe Biden as US president on 6 January.
Mr Hawley, an ally of Mr Trump, was the first senator to announce that he would challenge Mr Biden’s victory at the certification of votes in Congress, but was quickly joined by other Republicans including Texas senator Ted Cruz.
After a mob of pro-Trump rioters stormed the US Capitol during the certification of votes, causing House representatives to barricade themselves inside offices, Mr Hawley and Mr Cruz continued their challenge.
Seven Democratic senators called for an ethics probe into Mr Hawley and Mr Cruz in the wake of the riots, which saw five people die and several more injured, to investigate whether their objections led to the insurrection.
The Independent has contacted Mr Hawley’s office for comment, while the FEC said it could not comment and pointed to its guidance on personal use.