Tim Sale, a former health minister who retired in 2007, said some of Selinger's top staff, who have left their jobs to work for opponent Theresa Oswald's leadership campaign, have held a grudge ever since Selinger became leader in 2009.
The staff "have opposed and often undercut Greg Selinger from the outset," Sale wrote in a letter to the editor published in the Winnipeg Free Press.
The harsh words follow accusations last weekend from longtime NDP backbencher Rob Altemeyer. He said senior government staff who have left their jobs to work for Oswald are guilty of "an appalling abdication of responsibility."
The turmoil enveloping the NDP erupted in November, when Oswald and four other senior cabinet ministers stepped down from their portfolios after suggesting Selinger resign to stop the party's slide in opinion polls.
Instead of resigning, he said he was staying on and challenged his critics to run against him in a leadership contest, now set for March 8. He has stayed in the premier's chair while the leadership race unfolds.
Selinger's chief of staff told government workers they were free to work for any candidate without fear of retribution, and some have taken vacation time or left their jobs altogether to work on Oswald's campaign. The exodus included some of Selinger's top advisers such as Anna Rothney, head of the cabinet priorities and planning committee.
Rothney, who is managing the Oswald campaign, rejected the accusation she ever undermined Selinger. Rothney worked on Selinger's leadership bid in 2009 and said Thursday she and others who have now left the premier's office worked hard for him every day.
"That just hit us out of the blue," she said in reference to Sale's accusation.
"Staff had been committed to the premier 100 per cent."
Rothney pointed to several people helping to run the Oswald campaign who backed Selinger in 2009 and put in long hours on the 2011 election campaign that saw the party win a record 37 of 57 legislature seats.
The infighting has many New Democrats concerned that regardless of who wins the leadership vote, the party will remain divided and not survive a provincial election set for April 2016.
Gord Mackintosh, a veteran cabinet minister who has remained neutral in the leadership race, has offered to be a go-between to try to de-escalate the war of words.
"People in different camps have suggested that I might have a role to ensure party unity as this campaign unfolds, but just on an informal, unofficial (basis)."
Selinger faces two opponents in his battle to keep his job — Oswald, who served as health minister and minister for jobs and the economy; and Steve Ashton, a former transportation minister, who was not part of the internal revolt last fall.
Recent opinion polls have suggested a sharp drop in popularity for the NDP. A Probe Research survey last month suggested 26 per cent support for the New Democrats and 48 per cent for the Opposition Progressive Conservatives. Results from the random telephone survey of 1,002 Manitobans are considered accurate to within plus or minus 3.1 percentage points, 19 times out of 20.