Long-stalled legislation to loosen labor-organizing rules likely won’t be introduced next week, as a group of Democratic Senators continues tinkering with a proposal they hope can pass Congressional muster.

Sen. Tom Harkin (D-Iowa), who has led the negotiations with a cadre of swing-vote centrists and advocates of the Employee Free Choice Act, said he hoped to introduce a bill shortly after the July Fourth recess. But a Harkin spokeswoman indicated Thursday that the proposal might not be ready by then.

“Senator Harkin and his legislative staff are continuing to work on the bill and are making progress,— spokeswoman Bergen Kenny said.

The legislation, also known as “card check,— would allow workers to unionize through open-ballot elections.

While it is a top priority for labor unions and many Democrats on Capitol Hill, Republicans and business-minded groups are largely opposed, fearing the open-ballot process would unfairly intimidate workers and compel them to unionize.

And those opponents aren’t sitting idly by.

Republican Study Committee Chairman Tom Price (Ga.) will speak before the U.S. Chamber of Commerce on Tuesday to discuss his points of contention with the bill.

Conservative groups, for their part, recently ramped up their message machines in anticipation of a legislative fight this summer. The Employee Freedom Action Committee flooded the Nebraska media market this week with a $1 million ad-buy urging moderate Sen. Ben Nelson (D-Neb.) to vote against any compromise bill.

While Democrats will soon boast a 60-seat majority when Senator-elect Al Franken (D-Minn.) is seated next week, some in the Conference still have reservations about the legislation. So far, backers of the card-check legislation have been unable to corral enough support to advance the issue.

Indeed, Harkin spokeswoman Kate Cyrul noted Wednesday that “it’s going to be a heavy lift— to pass the bill, even with the filibuster-proof majority.

Sen. Arlen Specter (D-Pa.), who is among those trying to negotiate an agreement, announced before he defected to the Democratic Party in late April that he opposed the legislation in its current form. Nelson, who is not part of the negotiating group, also opposes the bill.

Sen. Mark Pryor (D-Ark.), also has reservations about the bill and is in talks with Harkin, along with Sens. Sherrod Brown (D-Ohio) and Charles Schumer (D-N.Y.), who support the legislation. Pryor’s state is home to the headquarters of Wal-Mart Stores Inc., one of the biggest corporate opponents of the legislation.

Just before the holiday break, on June 19, Brown offered a positive forecast for the legislation.

“We’re going to do something this summer. Stuff’s happening. We’re getting closer,— he said.