The U.S. Senate is expected to vote today on a campaign disclosure bill which Democrats say would bring more openness in political advertising and would force the backers of attack ads to be clearly identified.

Republicans, like Iowa Senator Chuck Grassley, oppose the measure, as it’s designed to counter a U-S Supreme Court ruling earlier this year that allows unlimited political spending by corporations, unions and other groups.

“The Supreme Court, back in 1976, said the ability to spend money is an extension of First Amendment freedoms,” Grassley says. “This bill would abridge First Amendment freedoms.”

In today’s vote, at least one Republican will need to side with the Democrats for the bill to survive, but Grassley says, no one from the GOP is expected to get on board. He fears the legislation will force a cutback in political advertising, which helps spark public debate on important issues.

“The more political discussion you can have, the better,” Grassley says. “We shouldn’t try to muzzle any sort of political discussion.”

The bill known as the Disclosure Act has already passed in the U.S. House. It would force corporations and nonprofit groups to provide more details about fundraising and their political spending, but Grassley says it goes too far.

“It’s intended to discourage political speech and my view is that we should have more, not less, political speech,” Grassley says. “It curbs it for the business community but it doesn’t curb it for the unions, so it’s very one-sided from that point of view.”

Grassley says he’s also against the bill as it would take effect right away. Usually, he says, this sort of regulatory bill doesn’t kick in until the following election year.

When the bill passed the House last month on a vote of 219 to 206, only two Republicans voted for the measure, while more than 30 Democrats joined most of the GOP in the opposition.