Attorney Zhang Qingfang said Friday authorities seemed to be in a rush, and that he was informed of the charges but hasn't seen the charging sheet, the Washington Post reported.
Beijing police filed their case with the prosecutor's office last Friday, alleging that Xu had disturbed public order by organizing demonstrations, Zhang said.
"Normally in a case like this, with 1,000 pages of material, it takes the prosecutor's office one and a half months to go over it" and file charges, he said. "I'm very surprised they handled it this fast. It is neither reasonable nor normal. It looks like it is just for show, and on orders from a higher level."
Xu, a legal scholar, founded the New Citizens Movement, which promotes rule of law and human rights. In March and April, several of the network's members held banners in Beijing calling on Communist Party officials to publicly disclose their assets. Since then, many members have been arrested.
Xu was arrested in July.
On Monday, Secretary of State John Kerry said the U.S. government recognized the five-year anniversary of the arrest of activist and Nobel Peace Prize laureate Liu Xiaobo, saying the United States was "deeply concerned" about the arrests of Liu and other activists "for peacefully exercising their universal right to freedom of expression."
"As the United States builds a constructive relationship with China, U.S. leaders will continue to raise concerns related to respect for the rule of law, human rights, religious freedom and democratic principles with their Chinese counterparts," the statement said. "We continue to believe that respect for international human rights is critical to China's growth, prosperity, and long-term stability."
China's Foreign Ministry rejected that appeal, arguing that both Liu Xiaobo and Xu Zhiyong had violated Chinese laws, the Post said.
"They deserve to be punished by law," ministry spokesman Hong Lei said during a regular news update Tuesday. "I need to emphasize that only the 1.3 billion Chinese people are best qualified to pass judgment over China's human rights condition."