You could call former New York City Mayor Michael Bloomberg and Facebook founder Mark Zuckerberg's silence over immigration reform before the mid-term elections a little puzzling.

As Politico reports today, none of the three largest immigration reform groups has plans to do any advertising on the issue in the months leading up to the November vote. Last year, they'd poured hundreds of thousands of dollars into such ads, supporting reforms.

The groups have substantial support from tech billionaires and other prominent business executives, and include Zuckerberg's, Bloomberg's Partnership for a New American Economy, and former U.S. Commerce Secretary and Citigroup vice chairman Carlos Gutierrez's Republicans for Immigration Reform.

Their reticence comes at a time when Republican leadership in Congress has refused to advance immigration reform, voted through in the Senate last summer with bipartisan support. Republicans have also amped up attacks on Democrats running for reelection, for being pro-amnesty.

So why the quiet? The fear of throwing money out the window, perhaps.

"Even the most optimistic of immigration reform proponents knows the chance of a legislative vehicle at this point is zero," says Emily Lam, vice president of health care and federal issues for the Silicon Valley Leadership Group, a technology company lobbying group that supports comprehensive immigration reform. In fact, SVLG is already planning a trip to Washington in December to express disappointment with Congress's inaction. 

Immigration reform is a big issue for Silicon Valley and the technology industry in general, where a shortage of qualified engineers and lack of a citizenship fast track for highly successful immigrant entrepreneurs could throttle innovation and job creation.

In Response to Congress' stonewalling, President Obama is expected to shape immigration policy with an executive order shortly after Labor Day. Among the things an executive order might do is to increase the number of green cards available to foreign workers in the U.S. by adjusting caps. 

"Right now, most advocates are focused on asking for executive actions with a list of items from the [President] anticipated in mid-September," Lam says.