Washington (CNN) -- Members of a key Democratic-controlled Senate panel cast the first congressional votes on a sweeping bipartisan immigration reform bill on Thursday, turning back the first GOP attempts to beef up the legislation's border security provisions.
The Senate Judiciary Committee met for eight hours, debating and holding votes on more than 30 proposed amendments.
A majority of the amendments were adopted, but no key provisions in the 844-page bill were significantly altered.
"When it comes to border security, for whatever reason, Democrats are going to be inclined to say it is secure and Republicans are going to be inclined to say it's not," said Sen. Lindsey Graham, R-South Carolina.
"I'm not blaming anybody, but that's the way this thing's going to break out in terms of votes."
Graham and Arizona GOP Sen. Jeff Flake -- part of the "Gang of Eight" senators responsible for crafting the bill -- sided with the committee's Democrats on the key votes.
The four Democrats and four Republicans in the "Gang of Eight" have promised to oppose any major changes to the bill.
"The gang stuck together, as we were told they would, on anything that's significantly impacting their legislation that they drafted with their friends," said Sen. Jeff Sessions, R-Alabama, a leading critic of the bill.
"I know it. And everybody needs to know it -- who's calling the shots."
Another member of the "Gang of Eight" on the committee, New York Democrat Chuck Schumer, urged his colleagues to "be constructive."
"Don't make an effort to kill a bill that is the best hope for immigration reform," Schumer said. This is the "best hope to (overcome) the partisan gridlock that has strangled the Senate, the Congress and the country."
Among the amendments rejected by the committee: a proposal from Sen. Chuck Grassley, R-Iowa, to block the legalization of any undocumented resident until "effective" control of the entire U.S.-Mexico border has been established for six months.
A majority on the committee also rejected a proposal by Texas GOP Sen. Ted Cruz to triple the number of U.S. Border Patrol agents along the Mexican border, while quadrupling the level of equipment and other assets along the border, including cameras, sensors, drones, and helicopters.
Cruz's amendment, similar to Grassley's, would have blocked any legalization of undocumented residents until "operational control" of the entire Mexican border has been established.
Flake and other opponents of Cruz's amendment argued it would cost tens of billions of dollars -- a fiscally irresponsible move when Congress is trying to cut deficit spending.
The bill as currently written commits additional resources to southern border security and establishes a new system of metrics to measure border control effectiveness, but critics insist the plan is full of holes and will ultimately do little to help stem to the tide of illegal immigration.
While claiming to strengthen the border, the legislation would also create a 13-year path to citizenship for most undocumented immigrants while bringing dramatic change to labor policy on America's farms.
If enacted, the plan would constitute the first overhaul of the nation's immigration policy since 1986.
Proponents say the change is necessary to permanently and fairly resolve the status of roughly 11 million undocumented residents. Critics insist the proposed change amounts to amnesty, rewarding those who chose to break the country's immigration laws.
The Judiciary Committee is set to continue its consideration of the "Gang of Eight" bill next Tuesday.