John Anton Blatnik (August 17, 1911 – December 17, 1991) was a United States Congressman from Minnesota. He was a member of the Minnesota Democratic-Farmer-Labor Party (DFL), which is affiliated with the Democratic Party.

Blatnik was born in Chisholm, Minnesota, to Slovene immigrant parents. He graduated from Winona State Teachers College (today Winona State University) and worked as a chemistry teacher in Chisholm.

From 1940 to 1944, he served in the Minnesota State Senate and volunteered to serve in the United States Army Air Corps in 1942. While in the Army Air Corps (the predecessor to the Air Force), he was chief of the Office of Strategic Services's mission with Tito's Yugoslav partisans for almost a year.

In 1946, Blatnik was elected to Congress representing Minnesota's 8th District in the northeastern part of the state, running on the newly unified ticket of the Minnesota Democratic-Farmer-Labor Party. He was reelected 13 times without much difficulty. He served in the 80th, 81st, 82nd, 83rd, 84th, 85th, 86th, 87th, 88th, 89th, 90th, 91st, 92nd, and 93rd congresses, (January 3, 1947 – December 31, 1974).

In 1963, Blatnik, introduced a bill to make Leif Erikson Day a nationwide observance. The following year Congress adopted this unanimously.

Blatnik voted for the Civil Rights Act of 1964. He was an early supporter of the Saint Lawrence Seaway and helped develop the original legislation to build it. He served as chairman of the Public Works Committee (now known as the Transportation and Infrastructure Committee) during his last two terms in Congress. As chairman, he shepherded the Federal Water Pollution Control Act, better known as the Clean Water Act, to passage in 1972.

Upon retirement, Blatnik endorsed his long-time administrative assistant, Jim Oberstar, to replace him in Congress; Oberstar won easily in the 1974 election.

In 1980, Blatnik was among the American delegation that attended the state funeral of Josip Tito held in Belgrade.