The suspended UK Border Force chief Brodie Clark has been treated with "contempt" by Home Secretary Theresa May, his union officials have said.
The First Division Association's Paul Whiteman said: "It is astonishing the home secretary [declared] him guilty before he had a chance of responding."
Mr Clark would comply with a request from MPs on the home affairs committee to give evidence to them, the FDA said.
Mrs May earlier told that committee she would not resign because of the row.
The home secretary allowed some checks on European travellers to be relaxed but says Mr Clark went further in scaling back checks, without her approval.
Answering questions from MPs about her involvement in the decision, she said Mr Clark must take responsibility for his "unauthorised actions".
The home secretary said she had not told the Cabinet of her decision to allow officials to relax checks on some European travellers arriving in the UK as the "limited" pilot was an "operational matter" which "did not in any way put border security at risk".
She said the idea was that at busy times it was safer to carry out "intelligence-led" checks on suspicious passengers rather than mandatory checks on all passengers, including those who were "low risk".
Labour committee member David Winnick suggested ministers should take full responsibility for a "major blunder" on their watch and asked if there was any question of Mrs May resigning - to which the home secretary responded: "No."
Mrs May said there were other procedures which prevented people from arriving illegally in the UK - including the e-Borders programme and the identification of potential threats by UK officers overseas.
She said she would take responsibility for the authorised pilot, which she suggested had led to a 10% rise in the detection of illegal immigrants, but Mr Clark must "take full responsibility for his actions".
Giving evidence to the liaison committee of senior MPs, Prime Minister David Cameron said there had been "activity going on by the UK Border Agency that was not acceptable".
But Labour shadow home secretary Yvette Cooper said it was "shocking" Mrs May was unable to say how many airports had relaxed checks over the summer - even under her own pilot scheme, which she authorised.
She said Mrs May should publish the guidance given to the UK Borders Agency and what information it provided to the Home Office.
"There is still a massive gap between what the home secretary is saying and what the guidance going out to Border Agency staff, even on her own so-called pilot, actually said," Ms Cooper said.
"It's a deep concern that what we have got is the home secretary blaming the officials a lot but still not being able to provide us with answers to the questions she should have asked."
Mr Clark is among three staff suspended. Mrs May has announced there will be three inquiries, the main one led by the Chief Inspector of the UK Border Agency, John Vine.
Mr Clark and Rob Whiteman, the UKBA chief executive, are to be called in front of the home affairs committee to answer questions about the matter.