Several federal watchdogs fired by Donald Trump have filed a lawsuit against his administration to get their jobs back.

In the suit filed on Wednesday, eight former inspectors general from eight government departments – including defense, veterans affairs, health and human services, state, agriculture, education and labor – and the Small Business Administration said they were seeking “redress for their unlawful and unjustified purported termination” by Trump and their respective agency heads.

The lawsuit states that just four days into his second term, Trump, “acting through a two-sentence email sent by the director or deputy director of the office of presidential personnel, purported to remove from office (supposedly on account of ‘changing priorities’) nearly a score of IGs”.

It also says that the fired officials were “appointed by and/or served under presidents of both parties”, including Trump during his first term.

Altogether, the inspectors general who were fired were responsible for conducting and facilitating oversight of more than $5tn of appropriated funds annually and more than 3.5 million federal employees, or 80% of the federal workforce.

The lawsuit alleges: “Despite the obvious illegality of these purported terminations, the head of each affected agency – including the eight heads of plaintiffs’ respective agencies – effectuated and continue to effectuate the purported removals.”

It adds that the eight federal agencies removed the inspectors general from their access to their government email accounts and computer systems, government-issued phones, personal ID cards and computers.

The inspectors general were also alleged to have been banned from entering the government buildings where they worked, with the lawsuit stating that “these actions have had their intended effect of making it impossible for the IGs to perform their lawful duties”.

“Because the purported removals were illegal and hence a nullity, the actions just described constituted illegal interference with the IGs’ official duties,” the lawsuit says, adding that “neither President Trump nor anyone else in his administration has claimed that the purported removals complied with the IG Act”.

“Instead, President Trump falsely claimed after the fact that such removals were ‘a very common thing to do’ and ‘a very standard thing to do’,” the lawsuit says, alleging that Trump is “wrong to claim these actions were ‘common’ or ‘standard’”.

As part of the lawsuit, the plaintiffs are seeking a declaration that their purported removals were legally invalid and so they remain as inspectors general of their agencies unless and until the president lawfully removes them in compliance with statutory procedures. Additionally, the plaintiffs are seeking injunctive relief prohibiting the defendants or anyone working in concert with them from impeding the lawful exercises of the duties of their office, the lawsuit says.

Wednesday’s lawsuit follows Trump’s sacking of 18 inspectors general less than a month after he returned to the White House.

Hannibal “Mike” Ware, one of the plaintiffs in Wednesday’s lawsuit and the former inspector general for the Small Business Administration, told MSNBC last month: “This is not about any of our individual jobs. We acknowledge that the president has the right to remove any of us that he chooses. But the protections that were baked into the act is everything, absent having to provide a real reason. We’re looking at what amounts to a threat to democracy, a threat to independent oversight, and a threat to transparency in government.”

Similarly, Mark Greenblatt, the former inspector general of the interior department, told CNN that the firings “should be setting off alarm bells”.

“The whole construct of inspectors general, it’s based on us being independent, that we’re not beholden to a political party of any stripe, that we are there as the taxpayers’ representatives to call balls and strikes without any dog in the fight. And so the question is: what will President Trump do with these positions? Is he going to nominate watchdogs or is he going to nominate lapdogs?” said Greenblatt.