MIAMI, May 31 (Reuters) - A Florida election law requiring third-party groups to turn in voter registration forms within 48 hours is "harsh and impractical," a federal judge ruled on Thursday.

U.S. District Judge Robert Hinkle blocked enforcement of that provision, but left intact most of the election law passed last year by the state's Republican-controlled legislature.

The League of Women voters had challenged the law, which carried a $1,000-a-day fine for failing to meet the time requirement. The group said the requirement was so onerous that it stopped holding voter registration drives in Florida. (Reporting by Jane Sutton; Editing by Anthony Boadle)