NEW YORK (AP) — Major League Baseball has started sending written warnings to players who have violated the new pace of game rules.

MLB spokesman Michael Teeven said Wednesday about 10 letters had been sent since the start of the season last weekend.

Penalties for violating the new rules include fines, which start May 1. Hitters are required to keep one foot in the batter’s box, with exceptions such as after foul balls. Pitchers in most cases are required to start innings before 30 seconds remain on the countdown clocks.