All five Power Five conferences have canceled their basketball tournaments, putting the NCAA Tournament in doubt.

The Big Ten, Big 12, SEC, ACC and Pac-12 conferences were all preparing to play games in large arenas across the country, but with few people in the buildings.

The NCAA had announced Wednesday that it planned to play its men’s and women’s tournament games that start next week with restricted access for the general public. The NCAA said only essential staff and limited family members would be allowed to attend the games.

The men’s NCAA Tournament is one of the most popular events on the American sports calendar. March Madness draws hundreds of thousands of fans to arenas from coast to coast.