"International organisations like the Red Cross, Israeli Arab parliamentarians and lawyers are forbidden from visiting the prisoners on strike," said Fedwa Barghouti, who like her husband is a senior member of president Mahmud Abbas's Fatah party.
"These Israeli measures are illegal and contravene the most basic of human rights," she said.
Lawyers had got Israel's Supreme Court to declare the ban illegal, but "were surprised to find they were still not permitted to visit detainees on the pretext that their health did not allow it," Barghouti added.
He was joined in the protest by more than 1,000 other Palestinian prisoners who say they will go without food until their demands ranging from better medical care to phone access are granted.
More From This Section
Yesterday, Palestinian NGO the Palestinian Prisoners' Club said Barghouti's health had declined seriously since the protest began.
Palestinian officials warned that if he gets worse, this could spark an "explosion".
Barghouti is popular among Palestinians, with polls suggesting he could win the Palestinian presidency.
Today, the committee that backs the hunger strikers called for a boycott on Israeli products and for trucks to be blocked from entering occupied Palestinian territory.
"Not buying Israeli products is the least every citizen can do to support the strike," it said in a statement.