The Guardian said on Wednesday that the incident happened earlier this year after the lawyers criticised their brief.
"The first day, when they were being briefed on the dos and don'ts, at least a couple said: 'You can't impose these restrictions on us because we can't properly represent our clients,'" the newspaper quoted a former military lawyer as saying.
"When the group decided they weren't going to go along, they were relieved. They reported in the morning and got fired that afternoon," added the lawyer, who was not one of those sacked in the incident.
The Pentagon's Office of Military Commissions denied the claim.
"That is not true, never happened," The Guardian quoted its
spokesman as saying.
Washington says the detainees, among 660 prisoners from 42 countries being held at the base in Guantanamo Bay, are all enemy combatants ineligible for due legal process and intends to have them tried in military courts.
"When the lawyers' group decided they weren't going to go along, they were relieved. They reported in the morning and got fired that afternoon"
Former military lawyer
Many of the prisoners were swept up during the US-led war that ousted the Taliban regime from Afghanistan in 2001 but none have been charged nor do they have direct access to lawyers.
The Guardian said Washington had put in place a new six-strong team of military defence lawyers but a "uniformed source" quoted by the left-wing daily said some were deeply unhappy at the nature of the planned trials -- believing them to favour the prosecution and an affront to modern US military justice.
"It's like you took military justice, gave it to a prosecutor and said, 'modify it any way you want,'" the source said.
Nine Britons are among the prisoners being held in Cuba but the British government insists it does not want them to face trial by military court.
Reports over the weekend said London and Washington would strike a deal by Christmas for the return of the detainees to Britain, where they would either face trial or be freed.
Meanwhile, US military officials told the latest edition of Time magazine that they were planning to release 140 of the prisoners.