Three alleged al-Qaida operatives have now chosen to boycott their upcoming trials and more are expected to do the same as the military attempts to prosecute dozens of Guantanamo prisoners at this isolated, high-security U.S. base overlooking the Caribbean.

Two men, a Saudi and a Yemeni, at pretrial hearings this week denounced the tribunals as a sham and said they would not cooperate with their defense or appear for future hearings.

Defense attorneys say they must uphold the wishes of their clients, and that they could face sanctions from the bar associations in their home states if they don’t.

Army Lt. Col. Bryan Broyles, defending an alleged al-Qaida operative, said he might have to be a “potted plant” during the trial.

Based on his client Ahmed al-Darbi’s decision Wednesday to boycott, “that should mean ... that I sit very quietly, answer the judge’s direct questions and that’s it,” Broyles told reporters.

Military judges have told lawyers that they must carry on with their defense even if their clients boycott. But Broyles said he “almost certainly” will file a challenge against the order that he defend his client in any case.

The chief prosecutor, Army Col. Lawrence Morris, said he does not know if the boycotts are organized but vowed to continue with the tribunals, also known as military commissions.

Even so, the boycotts have created an ethical dilemma and could slow trials that had been scheduled to begin in early summer — but are now widely expected to be delayed again. They may also create starkly one-sided proceedings.

“Without a credible defense effort, any convictions will simply fail to stand up to scrutiny in the court of world public opinion,” said David Glazier, a professor Loyola Law School in Los Angeles who has analyzed the U.S. military commission system.

So far, 15 detainees at Guantanamo have been charged. Of the five who have appeared before a judge, three have opted not to participate.