HARTFORD — Connecticut employers who try to intimidate immigrant workers by threatening to call federal authorities about their citizenship status could face stiff state fines and other penalties under a bill the Senate approved Thursday.

Sen. Gary Holder-Winfield, a New Haven Democrat who is one of the sponsors of the bill, said the legislation is intended to apply only to employers who “threaten to call immigration if [an employee] exercises his or her rights as a worker.”

The measure won unanimous Senate approval and now goes to the House for action.

State labor officials say they’ve encountered several cases of employers who try to use intimidation to keep immigrants — both legal and undocumented — from complaining to authorities about violations of their rights as workers.

“Many of these people are afraid to speak up,” Holder-Winfield told the Senate.

“Everyone has the right to speak up when conditions are wrong or when laws are broken,” said the Senate’s top Democratic leader, Donald Williams Jr. of Brooklyn.

“Far too often, when folks come to this country… they are at the mercy of unscrupulous individuals who would take advantage of them,” Williams said.

The bill would authorize state labor officials to hit employers who use such intimidation tactics on immigrant workers with a $100 fine for a first offense and up to $500 in penalties for repeated violations. The state also could close a business for between 30 and 60 days for threatening to call federal immigration authorities over a worker’s status.

Republican lawmakers, even though they ended up voting for the bill, said they were worried the potential penalties were far too harsh.

Sen. Joe Markley, R-Southington, said the bill’s proposed penalties “strike me as extreme punishment” for what he said were “broadly defined violations.”

He said that, for some businesses, being shut down for 30 or 60 days would be “a death sentence.”

Other Republicans said they worried that an employer trying to comply with federal laws forbidding employment of undocumented immigrants might end up violating these new restrictions simply by inquiring about a prospective employee’s status.

Sen. Michael McLachlan, R-Danbury, said part of the problem for Connecticut employers seeking to comply with federal immigration statutes is that “our federal administration is not enforcing these laws.”

Holder-Winfield said the bill’s penalties would only apply if a worker was being threatened because he or she was standing up for employee rights.