(Reuters) - A U.S. federal judge on Thursday blocked abortion restrictions in Alabama that limit how close clinics can be to public schools and ban a procedure used to terminate pregnancies in the second trimester.

Judge Myron Thompson in the District Court for the Middle District of Alabama issued a preliminary injunction, ruling that the laws are likely to be found unconstitutional, according to online court records.

The school-proximity law bans clinics within 2,000 feet of a K-8 public school.

Thompson wrote the law would likely force the closing of clinics in Huntsville and Tuscaloosa, where the majority of abortions in the state are performed, causing an undue burden for women seeking an abortion and other services.

"This burden would become particularly devastating for low-income woman" who would need to arrange lengthy trips to one of the other three clinics in the state for the same services, Thompson wrote.

Thompson wrote that Alabama's law restricting an abortion method commonly performed in the second trimester of a pregnancy, known as dilation and evacuation, also places an undue burden on women.

The law requires the doctor stop the heart of the fetus before abortion, an "inadequately studied, potentially risky procedure," he wrote.

The restrictions come amid a wave of laws being adopted by states as conservatives seek to chip away at the U.S. Supreme Court's landmark 1973 Roe v. Wade decision that legalized abortion.

In June, the U.S. Supreme Court struck down a Texas law imposing strict regulations on facilities that perform abortions.

Under the restrictions, Alabama could be left with three abortion clinics in a state where nearly one million women are of reproductive age, according to the ACLU of Alabama, which filed the lawsuit on behalf of the clinics.

State and ACLU officials were not immediately available for comment.

Alabama Republican Governor Robert Bentley signed the measures into law in May. The laws were to go into effect Aug. 1.

No other states have enacted limits on the proximity of abortion clinics to public schools.

(Corrects paragraph 4 to "undue" instead of "undo")

(Reporting by Brendan O'Brien in Milwaukee; Editing by Toby Chopra)