Local 100 of the Transport Workers Union is engaged in a meaningful and constructive debate with itself as the organization develops its latest negotiating position:

A burly transit union dissident has been charged with beating a union staffer aligned with Transport Workers Union Local 100 President Roger Toussaint, the Daily News has learned.

“This is a message for Toussaint,” assault suspect Christopher Magwood, 46, allegedly told victim James Mahoney during the incident at a Manhattan bus depot, Mahoney said yesterday.

Magwood — who is about 6-feet-3 and weighs around 300 pounds — was arrested this month on misdemeanor assault and harassment charges, Manhattan prosecutors confirmed yesterday.

He is a bus driver who sits on Local 100’s executive board. But Magwood has ties to a previous administration that lost power when Toussaint was elected, and he regularly opposes the union boss.

Mahoney — about 5-feet-5 and 180 pounds — works on retiree issues for Toussaint and organized protests leading up to last month’s illegal three-day transit strike.

The alleged TWU smackdown is among the topics the executive board is expected to discuss today at its first meeting since workers rejected a tentative contract deal by just seven votes this month.

The contract’s rejection highlighted dissent in the union, which has a history of tumultuous politics.

Mahoney, 56, was at the Quill Depot in Hell’s Kitchen on Nov. 15 to organize bus workers when, he said, he was attacked by a “ranting and raving” Magwood.

The bus driver shoved Mahoney’s head against the wall of an elevator, according to a criminal complaint.

“It hurt like hell,” Mahoney said yesterday.

Mahoney said he suffered bruises to his face and still has neck pain.

(Gratuitous On The Waterfront reference poached from here.)