Tui has joined in the legal action being taken against the Government by Manchester Airports Group, Ryanair, British Airways' parent company IAG and Virgin Atlantic.
The firm's UK and Ireland managing director Andrew Flintham said it has become an interested party in the action against the Government over its international travel traffic light system, the PA News agency has reported.
The risk-based system with red, amber and green ratings for different countries determines the quarantine and coronavirus testing requirements people face when returning to the UK.
The legal action being brought calls for more transparency over how Whitehall decides which countries qualify for the green list.
Speaking at the Travel Matters summit, Mr Flintham said: "At the time of the last country review, many destinations such as Malta, the Greek islands and the Balearics had much lower rates than the UK.
"It was an explicable as to why these were not added and instead Portugal was moved straight from green to amber, without the slightest sign of stopping at the much-vaunted green watchlist.
"We must understand the criteria we are all working towards so we can pre-empt when countries may move into different categories and help our customers with that challenge, and we must understand how the framework is being applied."
Abta chief executive Mark Tanzer told the conference that the organisation is also looking at whether legal action is "an avenue that we can pursue".
He said: "The hurdle for suing the Government is high but we think at least the Government needs to say, did it measure the impact on the travel sector of its own policies, and if it did, did it then decide that the sector nonetheless wasn't worthy of support?"
Mr Tanzer issued a "heartfelt plea for political change" in relation to restrictions on international travel.
Noting that outbound travel is influenced by several Government departments, he said the sector is not content to be "a political orphan".
He added: "Clear accountability for the welfare of the outbound travel sector needs to be given to a designated minister.
"Our economic contribution is weighty. More money is spent in the UK by British citizens prior to travelling abroad than is spent by international visitors, and the job creation or destruction potential is huge.
"I say to Government: put aside any misguided prejudices against outbound travel. We are ready to work together, show us that you are."
Mr Tanzer said Aviation Minister Robert Courts pulled out from a planned speech at the conference due to "a diary clash".
Mr Flintham said: "It is incredibly disappointing that the aviation minister didn't come to speak with us all today.
"There is no doubt the Government needs to hear what we have to say as an industry, and this once again feels like a sign that they're not."
