Loudoun County leaders expect to hear from more than 130 speakers Monday night at a public input session about the second phase of Metro’s planned Silver Line.

As the July 4 deadline for the Loudoun board’s deciding vote on the project approaches, both advocates and opponents of the Silver Line have heightened their efforts to be heard.

Last week, the conservative group Americans for Prosperity made thousands of robo-calls urging Loudoun residents to oppose the Metro extension, arguing that county taxpayers shouldn’t have to foot the bill for the project. The group said that it is planning to hold a rally outside the Loudoun County government center in downtown Leesburg Monday night.

Meanwhile, local business leaders and labor organizations have shown support for the Silver Line in recent weeks, running ads in local papers and urging Loudoun supervisors to consider the potential economic benefits of bringing Metro into the county.

Loudoun supervisors have a final scheduled work session Wednesday to address financing the project. Options presented by county staff so far include imposing a countywide commercial and industrial transportation tax or creating a special tax district for areas closest to the Silver Line.

Last week, Supervisor Matt Letourneau (R-Dulles) noted that the county could also opt to fund its $200 million commitment to the project without raising taxes.

Much of the uncertainty surrounding Loudoun’s participation in the second phase of the project centers on a project labor agreement proposed by the Metropolitan Washington Airports Authority. MWAA is expected to vote this week on whether to move forward with the union-friendly agreement, which has drawn the criticism of Loudoun leaders, as well as Virginia Gov. Robert F. McDonnell (R).

The first phase of the $6 billion Silver Line is under construction between Falls Church and Reston and is scheduled to be completed in late 2013.

If Loudoun supervisors vote to support the second phase, which would run to Dulles International Airport and into Loudoun, construction is slated to begin early next year.