A compromise on a key component of the Employee Free Choice Act (EFCA) could risk losing the votes of the bill's most ardent supporters, Rep. Phil Hare (D-Ill.) warned Wednesday.

Hare said that the binding arbitration component of the bill was a must-have element of the final version of the bill.

"WIthout that, you're taking the engine out of the automobile," Hare said in a conference call organized by American Rights at Work. "It looks nice but it's not going anywhere."

The arbitration provision would refer an employer and union to a federal mediator after 90 days of collective bargaining and invoke arbitration after 30 additional days, the decision from which would be binding for two years. Both parties could agree to delay those deadlines.

Hare said EFCA "may very well" lose votes if that section is watered down or removed.

"I can't speak for other people in the House, but I can say the people that I've talked to, including my committee chairman -- we're very locked in on this," he said. "But the people I know that support this bill, they want to see binding arbitration stay in the bill."

Still, Hare cautioned that he would have to see what compromises, if any, are made before deciding whether or not to hold his vote.

Arbitration has been somewhat of a hurdle in the Senate, where key centrist Democrats have expressed skepticism about the provision, making it difficult to attain the 60 votes necessary to overcome a filibuster and pass the labor legislation.