The bipartisan “gang of eight” senators insists it will be ready to unveil its much anticipated immigration bill in the coming week, despite skepticism from advocacy groups and critics.

They are “planning an announcement next week,” a senior Senate Democratic aide said on April 5, adding that significant progress has been made on the measure.

The aide said that the major provisions of the package have been agreed to and that the group’s time has largely been spent translating the agreement into legislative language, which has proved to be a time-consuming process.

Though Sens. Charles E. Schumer, D-N.Y., and John McCain, R-Ariz., two members of the immigration group, were scheduled to make a few media appearances over the weekend, the official bill unveiling will likely come later in the week, the aide said. But it was unclear whether the group would release its package before a pro-immigration reform rally scheduled for Wednesday, with thousands expected to attend.

The group has missed deadlines before and some advocates are not getting their hopes up.

“There is a lot of concern in our movement that delay is not a good thing,” said Frank Sharry, executive director of left-leaning immigration advocacy group America’s Voice, in a March 5 conference call. “We have tremendous momentum and the idea is, let’s build on that momentum by having a bill released” sooner rather than later.

The Senate group initially planned to release a bill before the end of March, but that finish line slipped to April, in part because of the end of March coincided with the two-week spring recess.

The delay has sparked angst among some advocacy groups, such as Casa In Action, which tried to keep the pressure on by protesting at Schumer’s Washington, D.C., offices last month.

Sharry said he believes the Senate group will produce a bill, but he said he wouldn’t be surprised if it isn’t unveiled until the week of April 15.

“It’s not like they are taking it slow or that there are major hiccups at this point,” Sharry said. “Its more a matter of doing the painstaking work of legislative drafting and review.

“We are still very optimistic that this bipartisan gang of eight is going to produce a bill that is going to be released. If it takes couple of days to get it done … I think it’s because they are trying to get it right,” Sharry continued.

Senate Judiciary Chairman Patrick J. Leahy, D-Vt., has said he wants to take up the bill as soon as possible to take advantage of the growing momentum for an immigration overhaul, including from the Republican National Committee and Republican Sen. Rand Paul of Kentucky.

But it’s unclear when the markup would be, given that six of the committee’s eight Republicans have requested a new round of hearings that could delay the bill from getting to the floor before the end of the summer. The other two GOP members of the committee — Sens. Lindsey Graham of South Carolina and Jeff Flake of Arizona — are members of the gang of eight.

Part of the problem, some Republicans contend, is that the bill is being drafted behind closed doors and they want to make sure they understand what’s in the package before the committee takes it up.

To that end, Sen. Charles E. Grassley, R- Iowa, the ranking member of the Judiciary Committee, and three other committee Republicans on April 4 asked the four Republican members of the gang of eight to make their staffs available to GOP committee staff by no later that Monday evening.

“The time for transparency has come,” Grassley said in the letter.

“Given the Majority’s rushed time table, we believe it is time for you to discuss the status of your negotiations, disclose what concessions have been made and provide details to members of the Judiciary Committee as well as the entire Republican Caucus,” the letter said.

Leahy has also raised concerns about the bill being drafted behind the scenes. And he has wondered out loud whether the Republicans’ desire for more hearings and concern for minority rights is a surreptitious effort to try to defeat the bill.

Nevertheless, the Vermont Democrat has also sought to assure Republicans that he wants an open and transparent process and intends to allow for ample debate time, in part to ensure the process does not become an excuse for opposition to the measure.

One signatory of the April 4 letter, Republican Sen. Jeff Sessions of Alabama, has been critical of Leahy and believes he plans to try to ram the bill through the committee.

In the letter, the four Republicans ask the immigration group to help ensure that their minority rights are preserved as the Senate considers the package.

The senators said in the letter that they “hope you will pledge your commitment to protecting the rights of the minority in the Senate by demanding a full, orderly and open debate process during Committee consideration and when the bill is sent to the full Senate.”

The senators also said they have concerns that Leahy has indicated he may hold only one more hearing, given that more than 40 immigration hearings have been held by the panel over the past four Congresses. The four senators would like what they say would be a more thorough process hearing from a wide variety of experts.

“Going forward, we expect to hear from experts on each of the proposals [within the bill] being put forth, including but not limited to a new temporary workers program, border security, interior and worksite enforcement, and the impact of a large-scale legalization on American workers and taxpayers,” the letter said. “We hope you will stand with us to ensure that all viewpoints are heard before the committee considers any immigration legislation.”

Advocates said any delay in introducing the bill could push floor action to June, instead of May as many have hoped. While there is some concern, advocates have not panicked yet, and they are still confident that a bill can get through the Senate and that they can put pressure on House leaders to take up a measure.

Still, the United Farm Workers of America claim the American Farm Bureau is using the bill to try to reduce wages of farm workers. The bill is expected to include a farm worker component.