The top Republican and Democrat on a congressional committee sent Gov. Rick Snyder a letter Thursday, inviting him to correct or supplement his sworn testimony in 2016 related to the Flint drinking water crisis and reminding him about federal perjury law.

But in a reply letter, Snyder told the lawmakers he testified truthfully and stands by what he said.

U.S. Rep. Trey Gowdy of South Carolina, the Republican chairman of the U.S. House Committee on Oversight and Government Reform, and U.S. Rep. Elijah Cummings of Maryland, who is the ranking Democrat on the committee, wrote to Snyder in light of sworn testimony earlier this month by a Snyder aide. That testimony contradicted what Snyder told the committee about when he learned of a spike in Legionnaires' disease cases in the Flint area.

Snyder, who testified under oath in Washington, D.C., when the lead contamination of Flint's drinking water was in the national spotlight, told the committee he learned about the Legionnaires' disease outbreaks one day before he made the health issue public at a Jan. 13, 2016, news conference.

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But Harvey Hollins III, who was Snyder's point person on the Flint water crisis, testified in a criminal case in Flint on Oct. 6 that he told Snyder about the Legionnaires' disease outbreaks weeks earlier, in December.

In the letter, Gowdy and Cummings cited details of the conflicting testimony.

"In order to resolve this discrepancy in recollection, please supply the committee with any additional relevant information you have concerning the date upon which you first learned of the Legionnaires' disease," the letter said.

"If necessary, you may also choose to amend or supplement your testimony."

The lawmakers asked Snyder to respond by Oct. 25 and told him that under federal law, it is perjury to "knowingly and willfully" make a false statement under oath.

Snyder wrote a reply letter to the committee Thursday, saying: "My testimony was truthful, and I stand by it."

"I have specifically reviewed the question and my answer referenced in your letter," Snyder said. "While you have offered for me to clarify my sworn testimony, I do not believe there is any reason to do so."

Snyder said he and his office "will continue to fully cooperate" with the committee.

Perjury prosecutions for lying to Congress are rare.

U.S. Rep. Dan Kildee, a Democrat from Flint Township, welcomed Thursday's letter from the lawmakers.

“Flint families deserve to know the truth about when the governor first learned of the Legionnaires’ outbreak," Kildee said in a news release. "Justice for Flint families comes in many forms, including holding those in state government who created the crisis accountable.”

Flint's drinking water became contaminated with lead following a switch of the city's drinking water supply to the Flint River in April 2014, while the city was under the control of a state-appointed emergency manager.

Despite almost immediate complaints about the color, odor and taste of the water, the state did not acknowledge a lead contamination problem until about Oct. 1, 2015, long after tests showed elevated lead levels in tap water samples and a spike in toxic lead levels in the blood of Flint children.

At least a dozen deaths have been linked to the Legionnaires' disease outbreaks in Genesee County that followed the water switch, though a definitive causal relationship between the water switch and the disease outbreak has not been established.

Contact Paul Egan: 517-372-8660 or pegan@freepress.com. Follow him on Twitter @paulegan4. Staff writer Elisha Anderson contributed to this report.