The Department of Immigration is calling in reinforcements for its new Australian Border Force, hiring a new squad of senior public servants in the wake of an exodus of its top managers.

Private sector consultants in Canberra have been hired to recruit assistant secretaries and first assistant secretaries, on salaries of up to $310,000, in the wake of the departure of 14 senior executives

The recruitment drive comes despite department boss Mike Pezzullo vowing to cull the numbers of top brass at Immigration before it merges on July 1 with Customs to create the "Australian Border Force".

It can also be revealed that Melbourne-based consultants were paid nearly $770,000 to vet Immigration senior managers for suitability to work at the new merged department.

The department's original plan was to shed large numbers, understood to be about 25 per cent, of Immigration's 119 senior executives with the survivors having to pass tough "Organisational Suitability Assessments".

But Immigration has been hit by some high-profile defections to other departments since the beginning of its takeover by Customs and arrival of the tough-talking Mr Pezzullo.

It has been reported that three deputy secretaries, two division heads, and at least two branch heads have departed in the wake of Mr Pezzullo's appointment as Secretary.

Now Canberra recruitment firm Ford Kelly have been hired to find "highly talented, motivated individuals for leadership positions across the organisation" to fill SES Band 1 and 2 jobs, working in various areas across the 13,000-strong merged department.

A contract worth $769,000 with Melbourne consultants NGS global, understood to be for undertaking the vetting process of senior executives, was notified on the official AusTender website in December.

The private sector hiring process is expected to cost another several hundred thousand dollars but a departmental spokesman said the figures were not available.

She confirmed the new high-level recruits were being drafted in to fill gaps left by recent departures.

"Since September 2014, 14 SES officers across the portfolio have retired or transferred to other APS agencies," she said.

"As a result the portfolio has undertaken a recruitment exercise managed through an executive search agency to replace specialist skills lost through these retirements and transfers.

"The cost of the recruitment process is consistent with SES recruitment activities.

"The information is not available as the process is yet to be finalised."

The spokeswoman confirmed that all SES had been put through the vetting process but the department has previously confirmed that none of its top managers had been shown the door as a result.