What are the changes that came in last week?

The Australian Border Force Act took effect on Thursday, creating a new body that merges the frontline operations of the Immigration Department and Customs. In the words of Prime Minister Tony Abbott, it will "ensure the legitimate passage of people and goods through our borders while preventing all illegal passage".

Perhaps most controversially, the Australian Border Force Act includes new guidelines for how its staff must conduct themselves – with a heavy focus on secrecy. It says those "entrusted" within the Border Force regime – including doctors, teachers and social workers employed in detention centres – could face two years' jail if they disclose confidential information.

Under the changes, which were supported by the Labor opposition, a professional who works in an immigration facility can speak out only if they have been given departmental approval.

What has been the response?

Doctors, nurses, teachers and contractors who work in immigration facilities expressed their outrage. In an open letter to Mr Abbott, Immigration Minister Peter Dutton and Opposition Leader Bill Shorten, more than 40 former detention centre workers challenged authorities to prosecute them for publicly discussing conditions in centres.

Mr Dutton responded that their claims were inaccurate, and that contractors would still be able to speak out about the conditions under the Public Interest Disclosure Act. That act says a public interest disclosure can be made only if a person believes that there is "substantial and imminent danger to health, safety or the environment".

Mr Dutton says the controversial bit of the new border force act will protect "sensitive operational information from unauthorised disclosure", but that it will not restrict anyone's ability to raise genuine concerns about conditions in detention should they wish to do so through "appropriate channels".

There has been no mention of what these appropriate channels could be, but the media is unlikely to make the cut.

What will the impact be? Are the changes likely to lead to people being charged?

New Australian Border Force commissioner Roman Quaedvlieg said it was highly unlikely people would be charged or jailed for speaking out.

That said, the legislation has been clearly designed to intimidate workers to not speak out, or disclose sensitive information. It will become much harder for workers or contractors to openly criticise conditions in detention centres, particularly on Nauru and Papua New Guinea's Manus Island.

Last year, former immigration minister Scott Morrison used Section 70 of the Crimes Act to refer a number of Save the Children staff working on Nauru to the Australian Federal Police, essentially for leaking information. The staff were cleared of the allegations by an inquiry long after they had been removed from the island. This strategy is something that could be easily used against immigration and contractor staff under the news laws.

Why has Mr Abbott brought in a border force commissioner?

As described by the government, the Australian Border Force has been introduced to protect and secure Australia's borders. Many commentators believe it has been modelled on the US Department of Homeland Security. They say it is militarising immigration, and pushing the Immigration Department far from its role of resettling refugees.

In a recent press statement, Mr Dutton said the border force would undertake "operational responsibilities". They include intercepting prohibited imports at the border, immigration compliance and "maintaining the good order of Australia's detention facilities".

Former workers in the Immigration Department have described the current atmosphere in the department as toxic.

A recent Senate Estimates hearing was told 15 elite senior staff had left the Immigration Department since new secretary Mike Pezzullo was sworn in late last year.

Asked about the departures, the department told Fairfax Media: "Through a recent recruitment process, the department has taken the opportunity to refresh the leadership cohort and renew the focus required to support the portfolio through its recent recruitment process".

What will the commissioner do, and who will he replace?

Commissioner Quaedvlieg was previously the head of Customs. Mr Pezzullo will remain as the secretary of the Immigration and Border Protection Department and will "work closely" with Mr Quaedvlieg.

Mr Quaedvlieg said he would look after the operational side of immigration, including targeting visa overstayers, unscrupulous migration agents, narcotics traffickers, people smugglers and everyone in between.

At a press conference last week, he said that operational security was "paramount" to conducting effective and tactical operations. That meant he would continue the practice of not releasing information about what the government calls "on water matters".

"I don't intend to stray from the current position in relation to operational security in relation to Operation Sovereign Borders," he said.

The Australian Border Force will also work closely with the Australian Federal Police to target national security threats, with dedicated counterterrorism units at Australia's major airports.