Tax return day very nearly took the life of House Democrats’ signature tax simplification initiative, as conservative Democrats continued to defy House leadership’s requests on handling procedural votes.

A measure that would have killed the Taxpayer Assistance and Simplification Act of 2008 failed on a 210-210 tie vote, despite vote-shifting after the clock ran out. Twenty-one Democrats voted for the measure, which also would have changed the tax bill to prevent illegal immigrants from getting tax breaks.

The tie vote came with some procedural wrangling. The vote was held open with the clock at 0:00 as the narrow margin fluctuated by a vote or two. Rep. Lee Terry (R-Neb.) walked to the desk with a red card to change his vote to no, as Republicans sought additional supporters. He later changed his vote to yes.

In addition to Terry, The Congressional Record indicates that Reps. Michael Burgess (R-Texas) and Mark Souder (R-Ind.) changed their votes from no to yes on the Republican motion. Reps. Anna Eshoo (D-Calif.), Tom Allen (D-Maine), Robert Brady (D-Pa.), Jerrold Nadler (D-N.Y.) and Susan Davis (D-Calif.) changed their votes from yes to no.

The vote was gaveled closed by Rep. Sheila Jackson Lee (D-Texas) in the Speaker’s chair after someone on the Democratic side shouted, “Shut it down, Sheila.”

Rep. Gary Ackerman (D-N.Y.) was walking toward the desk with a green card when the vote was gaveled closed.

Rep. Lynn Westmoreland (R-Ga.) pressed a point of parliamentary inquiry, hinting that he believed Democrats had broken House rules by holding the vote open to reverse the outcome. But Westmoreland did not raise a direct challenge.

Democrats who voted for the measure and against their leaders included Reps. John Barrow (Ga.), Melissa Bean (Ill.), Dan Boren (Okla.), Joe Donnelly (Ind.), Brad Ellsworth (Ind.), Kirsten Gillibrand (N.Y.), Baron Hill (Ind.), Heath Shuler (N.C.) and Zack Space (Ohio).

Three Republicans from South Florida voted with Democrats on the motion. GOP Reps. Lincoln Diaz-Balart, Mario Diaz-Balart and Ileana Ros-Lehtinen face their first serious reelection challenges from Democrats this fall, and all three represent districts with large Hispanic-American populations sensitive to immigrant-bashing.

The tax bill would end a private tax collection program and prevent federal contractors from avoiding payroll taxes by hiring American employees through offshore shell companies. The Boston Globe has reported that KBR, a former Halliburton subsidiary, avoided paying Social Security and Medicare taxes for American employees working in Iraq by hiring them through Cayman Islands shell companies.

The Republican motion would have tried to stop illegal immigrants from claiming the Earned Income Tax Credit and sought to block subsidies from going to so-called “sanctuary cities” that don’t enforce immigration laws.

Democratic House leaders have been wrestling for at least a year with how to handle the procedural motions, called “motions to recommit,” that the Republican minority has thrown at them.

Just before the Easter break, an angry House Appropriations Chairman David Obey (D-Wis.) told members not to ask him to meet with their local delegations if they won’t vote with leadership on procedural motions.

He then canceled a meeting with a Louisiana delegation after Rep. Charlie Melancon (D-La.) voted against a procedural motion connected to the House ethics bill.

House Republicans have flummoxed Democrats at times with their campaign of procedural votes that they say are intended to “make vulnerable Democrats choose every day between Speaker [Nancy] Pelosi [D-Calif.] and their constituents.” They inject controversial, unrelated issues, such as gun rights or immigration, into complex legislation being shepherded by Democrats.

Republicans say they’ve passed 24 such motions on the House floor since the start of this Congress.

They say two such motions have been passed into law and several other bills have been pulled from consideration when leaders fear they don’t have the votes.

When Republicans controlled the House, their leaders demanded members uniformly vote against such procedural motions.

Democratic leaders have a two-pronged approach to party discipline on the procedural votes.

They don’t object when members vote for procedural motions that simply amend the bill, but they have repeatedly asked members to vote against motions that they say kill the bill by sending it back to committee. In procedural parlance, the killer amendments order a committee to report back only “promptly,” instead of immediately or “forthwith.”

Republicans say that sending the bill back to committee does not kill the bill. House Majority Leader Steny Hoyer (D-Md.), however, argues it does because the recommitted bill undergoes a long delay and is likely to simply be sent back to committee the next time it comes up.