The Department of Homeland Security has asked U.S. Border Patrol Chief Mark Morgan, a former longtime Federal Bureau of Investigation agent, to step down from his post.

News of his departure, expected within a month, comes as the Trump administration moves toward tougher enforcement of immigration laws.

Two sources familiar with Morgan's departure told Reuters that he held a morning phone call with employees to say that he was not resigning – but had been asked to leave by the Trump administration.

Morgan's ouster also comes the day after President Donald Trump announced a broad plan to crack down on border security, including directing the construction of a wall along the border with Mexico.

Mark Morgan, chief of the US Border Patrol, is on his way out after the Trump administration told him to step aside

President Donald Trump, an immigration hard-liner, signed an executive order on Wednesday directing the Homeland Security Department to erect a wall between the U.S. and Mexico

The border patrol union, which endorsed Trump's presidential campaign and applauded his executive order, had been critical of Morgan. The union criticized Morgan for supporting former President Barack Obama's plans to shield certain illegal immigrants from deportation through a White House-driven amnesty.

The executive board of the National Border Patrol Council called Morgan arrogant and a 'disgrace to the Border Patrol' in an opinion piece published by Breitbart.com on Nov. 30.

Unlike many border patrol officers, Morgan did not climb the chain of command within the agency but was appointed from the FBI.

Morgan was named to the post in June and took office in October. The former FBI agent briefly led the internal affairs department at the Border Patrol's parent agency before heading the agency of roughly 20,000 agents.

In a statement, Kevin McAleenan, the Customs and Border Protection's acting commissioner, praised Morgan for 'his unwavering dedication to our border security mission' and 'lifelong career in service to the nation.'

Morgan was the first outsider to lead the agency since its founding in 1924. He clashed with rank-and-file officers in the Trump-friendly union from the start.

Rank-and-file Border Patrol officers applauded on Wednesday as Trump spoke before the Homeland Security Departmentswearing-in of new Secretary Gen. John Kelly

Trump wants thousands of miles of 'impenetrable' barrier to stop the flow of drugs, illegal immigrants, and trafficked people coming across America's southern border

A former official told the Associated Press that Morgan was not at work on Wednesday and did not attend a gathering at the Department of Homeland Security with Trump and newly appointed Secretary John Kelly.

During that visit Trump singled out the union's president, Brandon Judd, while pointedly avoiding mention of Morgan.

Judd served on Trump's transition team.

The union was incensed when Morgan told a Senate hearing Dec. 1, in response to a question from Delaware Democratic Sen. Tom Carper that he supported a comprehensive immigration overhaul, which is often interpreted to include a path to citizenship for people who are in the country illegally.

Morgan clarified his remarks in a note to Border Patrol staff the following week.