The letter said Zhang and his wife were willing to be investigated by the family planning committee in Chen's hometown, the eastern city of Wuxi, and would accept whatever penalty the couple might incur. It did not provide details on how the couple had been able to evade family planning authorities thus far.
Officials from the family planning office of Wuxi's Binhu district told state media Sunday that the couple had sent representatives to the office to accept an investigation and that it was under way.
But Zhang's office also rejected reports that he had fathered more children. It said unidentified individuals with "ulterior motives" had sent people to follow Zhang's children and photograph them and that Zhang's office reserved the right to take legal action.
Known to many as China's one-child policy, the rules limit most urban couples to one child and allow two children for rural families if their firstborn is a girl. The government introduced the policy in 1979 as a temporary measure to curb a surging population, but it is still in place despite being reviled by many citizens.
Last month, the party announced that it would allow couples to have two children if one of the parents is a single child, the first substantial easing of the one-child policy in nearly three decades.