Louisiana’s senior U.S. Sen. David Vitter is among a trio of senators who have launched a probe into the Environmental Protection Agency’s handling of the water quality crisis in Flint, Michigan.

Vitter, Sen. James Inhofe (R-Okla.) and Senate Majority Whip John Cornyn (R-Texas) sent a letter to the EPA, demanding information about when the agency became aware of the city’s lead-tainted water supply.

“It certainly appears that the EPA did not take action, or at a minimum, alert citizens about the lead contamination,” the senators wrote.

Vitter, a Republican and a senior member of the Senate Environment and Public Works Committee, has represented Louisiana in the Senate since 2005. He has said he won’t seek re-election this fall.

Vitter, Inhofe and Cornyn are seeking access to internal EPA correspondence about the water crisis, as well as information about briefings that the agency held on it.

Read the letter here (PDF).