Alberta Progressive Conservative leadership hopeful Jason Kenney will resign as an MP next week.

Kenney, who wants to unite the right in provincial politics, will officially step down on Sept. 23, his campaign confirmed Tuesday.

"I am leaving my seat in the federal Parliament to do everything I can to advance the cause of unity so we can defeat the NDP, and get our province back on track," he said in a written statement Tuesday.

"The only way for [a party merger] to happen is if the PCs elect a leader that will support a merger, negotiate in good faith with the Wildrose Party, and seek a mandate from grassroots members of both parties in a referendum."

An MP for 19 years, Kenney has been under fire for collecting leadership donations while still sitting as a federal politician.

The campaign said Kenney had committed from the start that he would leave his job as an MP in October, but moved the date forward simply to pack up his office and tie up loose ends in a job he has held since 1997.