The act would expand amendments first added to the Export Administration Act in 1977, initially to protect American companies from the Arab League boycott of Israel.

Supporters of the measure dispute critics who say it would stifle pro-Palestinian activism.

“These kinds of First Amendment issues were not raised in ’77,” said Stuart E. Eizenstat, the chief White House domestic policy adviser during the Carter administration when the amendments were negotiated. “Since it’s come up here, in many ways, this legislation is stronger in protecting First Amendment rights because it explicitly indicates that political views are protected.”

The bill sponsored by Mr. Cardin and Senator Rob Portman, Republican of Ohio, was conceived after the United Nations Human Rights Council announced that it would create a database of companies that have business in the West Bank and the Gaza Strip, whose governance and status have been in dispute since the Six Day War in 1967.

“From our perspective, we have to protect U.S. companies from being put in a position that could harm them,” Ms. Walitsky said.

The bill, which would impose penalties on boycott participants, has already been modified after complaints from the A.C.L.U., which does not publicly take a stance on the Israeli-Palestinian conflict, about the infringement on First Amendment rights. Supporters of the legislation say that the language does not prevent companies and individuals, independent of direction from foreign countries or international agencies, from announcing their intent to boycott Israel.

“Our bipartisan legislation is a direct response to highly selective and discriminatory efforts to isolate Israel, such as those by the U.N. Human Rights Council,” Mr. Portman said in a statement.

But the changes, which most notably reduce the most significant penalty for participation to a fine of up to $1 million, were not seen as sufficient by critics, who scorned efforts to wrap a final version into a spending package without public debate.