The disclosure is directed to a clamp for connecting a ledger to a shoring post. The clamp includes a base member, a ledger-connecting member, and a first jaw, which are fixed connected to each other. The clamp includes a rotatable member inserted into the base member, which is rotatable and slidable in the base member along a longitudinal axis. A portion of the rotatable member is accessible via the slot of the base member. The clamp includes a second jaw fixedly connected to the rotatable member. The clamp further includes a wedge, and when the wedge is inserted into the slot of the base member to engage the rotatable member in a lock position, the first and second jaws are locked to capture two sides of a shoring post.