FISHERMEN have demanded the right to operate illegal passenger services to China to supplement their incomes, despite warnings from the Immigration Department. The department last month issued a directive to all boat owners to observe immigration regulations before carrying passengers out of Hong Kong waters. The move followed media reports of a security blind spot in southern waters where some local fishermen were operating daily tours to Lingding Island, a China-owned islet six kilometres from the territory. The services were unhindered by immigration or customs checks, raising concern that they could carry criminals, firearms, and other contraband to and from China. An Immigration Department spokesman said yesterday warnings had been issued to local boat owners last month. ''We have advised boat owners of the proper procedures and from now on there can be no excuse and they will face prosecution and a maximum fine of $20,000 on conviction,'' he said. But the Cheung Chau Fishermen's Welfare Promotion Association chairman To Kwong-biu accused the department of making a fuss and feared it could make fishermen's life more difficult. ''It is no big deal at all. We are not smuggling firearms. We are carrying visitors to Lingding to have fun,'' Mr To said. He believed most fishermen would ignore the warning and continue their businesses as usual.