The Immigration Department at Belconnen.

• More public service news

Up to 25 senior managers at the Immigration Department will learn the news of their sackings within weeks, DIBP has confirmed.

The long-feared purge of Immigration’s Senior Executive service by their new boss Mike Pezzullo is expected in early February with up to 20 per cent of the department’s SES expected to be shown the door.

The sackings will come as the department prepares for the emergence of “Australian Border Force”, which will see Immigration merged with Mr Pezzullo’s old agency, Customs, to create the new entity.

Senior Immigration managers and their new colleagues from Customs  have been undergoing “assessments” for several months since soon after the merger was announced and will learn their fates in early February, with Mr Pezzullo himself expected to make the final decisions.

Insiders expect the casualties to be heaviest at Immigration as part of what is being called the “Customisation” of the department and a “reverse takeover” by the smaller Customs agency.

Do you know more? Send confidential tips to ps@canberratimes.com.au.

In addition to the purge of the top ranks, about 100 of Immigration’s 530 middle managers at Executive Level 2 classification are expected to be clearing out their desks by the end of 2015.

In recent months Immigration’s 8500 public servants have been told they will be breathalysed and drug tested and must make detailed personal disclosures to satisfy a new Organizational Suitability Assessments or face the sack.

There will also be a crackdown on second jobs, social media use and sloppy appearances among the department’s public servants, as the Customs agency hierarchy tightens its grip on Immigration.

A departmental spokeswoman confirmed on Monday that the senior executives in Customs and Immigration would learn their fate early in February.

“SES staff in both the Department of Immigration and Border Protection and Customs and Border Protection have been engaged in an ongoing process of assessment and feedback,” she said.

“The future organisation structure and placement of staff is in development and will be communicated with the SES in early February.”

Immigration’s staff headcount shrank by 600 last year but the number of senior executives, who earn between $162,000 and $310,000, remained steady at 119.

Customs reduced its headcount by about 158 in 2013-14 but the ranks of senior executives swelled from 59 to 65, despite undergoing its own transition process during the year.

Senior executives at Customs earn between $147,000 and $283,000 a year, although they may benefit from performance bonus payments not available to their counterparts at Immigration.

Wage disparities and cultural differences between the two agencies will be among some of the challenges to be overcome as the formation of “Border Force”, due in July 2015, draws closer.