The pro-establishment DAB party has warned that China may well hit back at the United States if Congress passes the Hong Kong Human Rights and Democracy Act.
Anti-government protesters have been urging the US to pass the bill, which would oblige Washington to make annual assessments of Hong Kong's level of autonomy to decide whether it should keep its separate status from that of the mainland.
The act could also lead to sanctions against top officials who undermine Hong Kong's freedoms.
But DAB chairwoman Starry Lee and party lawmaker Holden Chow said on Tuesday that they had told US Consul General Hanscom Smith that Beijing and the SAR government could retaliate if the act is passed.
Lee and Chow said they met Smith earlier in the day and urged him to press Washington not to support the bill.
"I don't know what the response from the central government and the Hong Kong SAR government will be if it's passed finally. But of course, we cannot rule out any possiblity. I think it's a very logical way to think that the central government may have some kind of response, including doing some anti-measures against the act," Lee said.
She also added that the bill amounts to interference in the SAR's affairs.
"Using domestic legislation to affect a foreign jurisdicition is inappropriate," Lee said.
Last week, Chief Executive Carrie Lam also warned that the US Congress could not be allowed to become "a stakeholder in Hong Kong's affairs".