Updated at 6:30 p.m. with comment from the Cruz campaign.

WASHINGTON — Sen. Ted Cruz’s Senate campaign committee has received three letters from the Federal Election Commission this election cycle for accepting campaign contributions that exceeded federal limits.

The FEC sent the "Ted Cruz for Senate" committee letters in September, April and June. The letters were first reported by the Houston Chronicle.

Cruz's campaign has received the most notices of excessive contribution out of 32 Senate campaigns, according to an analysis by the Chronicle.

Brett Kappel works on FEC compliance cases as an attorney, and said it is rare for Senate campaigns to receive repeated notices of contribution limit violations. However, he said the letters to Cruz’s committee have been from the FEC’s reporting analysis division, not its enforcement division.

“Normally it’s not a significant factor, but in some cases it can become an issue,” Kappel said. “They’re not there yet.”

The letters named dozens of individuals and one political action committee that gave to the Cruz campaign above the $2,700 individual contribution limit per election and the annual $5,000 PAC limit.

Cruz’s committee responded to the first two FEC inquiries by reattributing donations to donors’ spouses, redesignating contributions from the primary to general election race, returning money to Cruz’s joint fundraising committee, and refunding some donations.

These are legal methods of complying with campaign finance law.

The Cruz campaign committee has until July 26 to respond to the FEC’s latest letter, and the FEC filing deadline for the second quarter of 2018 is July 15.

The Chronicle found three other Senate candidates who received one notice each this cycle citing contributions over federal limits: Sens. Bob Casey, D-Pa., Dean Heller, R-Nev., and Tammy Baldwin, D-Wis.

Part of the reason for Cruz’s reported excessive contributions could be the structure of online contributing on his website.

Donors are enrolled to give automatic monthly contributions unless they opt out. These monthly payments may not stop when contribution limits are reached.

Kappel said the norm in online campaign fundraising is to allow users to opt in to monthly donations.

Many of the contributions cited by the FEC were small, repeated contributions made by individuals. Cruz campaign spokeswoman Emily Miller said in a statement that the campaign is "blessed with very passionate supporters, many of whom give us $100 or so every single month to help our campaign fight the liberal Beto O'Rourke and the fake news media."

"Some of them are on the team so long that they eventually exceed the contribution limit with their recurring donations, which is obviously when we refund any funds that are above that limit in accordance with campaign finance guidelines," Miller's statement continued.

Brendan Fischer, the director of federal reform for the Campaign Legal Center, said the Cruz campaign committee’s citations were unusual because some individuals exceeded limits in more than one instance.

“They should have the controls in place to stop the automatic donations when the limits are reached,” Fischer said.

Cruz’s challenger in November, El Paso Democrat Beto O’Rourke, has not received notices from the FEC flagging excessive contributions.

O’Rourke posted record-setting fundraising numbers last quarter. He doubled Cruz’s contributions by pulling in $6.7 million to Cruz’s $3.2 million, though Cruz’s haul was strong for a typical incumbent.

O'Rourke has refused to accept PAC money for his race. He previously took PAC money, according to campaign finance tracker OpenSecrets.org.

Cruz’s fundraising numbers include his principal campaign committee, a joint fundraising committee, and a leadership PAC named the “Jobs, Freedom, and Security PAC.”