WASHINGTON (AP) — The Senate's top Republican says the chamber will cast a key test vote Wednesday on the party's long-awaited tax overhaul.

Majority Leader Mitch McConnell said the Senate "will vote to begin debate on this once-in-a-generation opportunity to reform our tax code so it works for the middle class."

The Kentucky Republican and other top lawmakers toiled behind the scenes to line up stragglers. A controversial "trigger" mechanism that could pare back some of the measure's corporate tax cuts was being shaped behind the scenes.

At the same time, a pair of GOP senators proposed making a $2,000 per child tax credit more widely available to low-income earners.

McConnell urged Republicans who have reservations about the bill to vote to begin debate so they can offer amendments to improve it.