Pro-democracy activists have accused Chief Executive Carrie Lam of slicing away at Hong Kong like salami with the SAR's involvement in the Greater Bay Area initiative.
Around eight members of the League of Social Democrats (LSD) staged a protest on Thursday outside the venue where Beijing officials and the SAR government held a symposium on the plan.
The group said Hong Kong will not benefit at all from the bay area integration and only the mainland stands to gain anything.
Former LSD lawmaker Leung Kwok-hung said the CE has betrayed Hong Kong "for the fame".
"Bit by bit, Carrie Lam will just cut Hong Kong into many slices, it's like a salami," Leung said.
He told RTHK's Joanne Wong that the government has sold out the SAR by using taxpayers' money to sponsor infrastructure that benefits the mainland, such as the new bridge and express rail line, putting Hong Kong's economy under Beijing's control.
Another 30 people also protested outside the venue on Thursday morning, complaining that they had lost hundreds of millions of dollars in a property project in the Greater Bay Area.