Paul O’Connor, of the Public and Commercial Services (PCS) union that represents Border Force and Home Office staff said he was “ruling absolutely nothing out in terms of responses to look after the welfare of our members”.
The union has already been a key part of legal action against the Rwanda deportation policy, which is still going through the courts.
Mr O’Connor said that if the legal action fails, PCS union members would look to industrial action to try and stop the plan.
He told The Independent: “The Government is fighting a losing battle, not just on the policy issue itself but with its own workforce who they’re going to task with implementing it,” he told The Independent.
“There will be no stomach amongst our members for implementing the Rwanda deal and Illegal Migration Bill, and they will inevitably come to their trade union to see if there is recourse to stop it happening.
“If any litigation fails, they will want to explore with us whether there’s an industrial solution.”
Mr O’Connor said the “environment of hostility” against asylum seekers created by the government was also damaging civil servants’ mental health.
“It makes their working lives extremely unpalatable,” he added. “They feel if they were put in a position where they had to carry out an act that was subsequently proved to be unlawful, they themselves might be open to prosecution.”
A Home Office spokesman said: “Our staff work tirelessly to deliver ground-breaking policies, such as the Illegal Migration Bill.
“This will reform our immigration system and stop the boats, while still remaining party to the European Convention on Human Rights.
“We have always maintained that the UK and Rwanda Migration and Economic Development Partnership is lawful, including complying with the Refugee Convention, and last year the High court upheld this.
“We stand ready to continue to defend the policy against legal challenge.”
It came as the United Nations’ refugee agency has identified significant failings in the UK asylum system, warning that officials were being forced to do “too much, too quickly, and with inadequate training”.
The UNHCR said it had either seen or been informed about “numerous risks to the welfare of asylum-seekers”, with trafficking cases overlooked and victims of torture being detained.
The comprehensive audit of the system praised Home Office staff for their work under difficult conditions, but said that corners were being cut and workloads were unsustainable.
The Home Office said “significant improvements” had been made since the audit was carried out in 2021 and early 2022.
“The current registration and screening systems expect staff to do too much, too quickly, and with inadequate training, facilities, guidance and oversight. As a result, much of their hard work is wasted, and the system frequently fails to achieve its goals,” the UNHCR audit said.
The report said that the UNHCR “observed or was told about numerous risks to the welfare of asylum-seekers, including instances of trafficking and vulnerability being overlooked and teenage children and victims of torture and trafficking being detained”.
“Registration and screening records were often incomplete, inaccurate, or unreliable, and laws and published policies were not complied with.”
The review said “central aspects” of screening interviews were routinely delegated to interpreters, there were no formal quality assurance systems and different practices were followed in different locations.
“For all of these reasons, there is a real risk that decisions based on information collected at screening will be flawed,” the report said.
The UNHCR said rules to make an individual’s asylum claim “inadmissible” if they came through a safe third country and the plan to send some asylum-seekers on a one-way trip to Rwanda made the reliability and fairness of the screening system more important.
It warned that making decisions on who is sent to Rwanda using the same screening process “will lead to errors, causing distress to individuals, delays, and well-founded litigation”.