Washington (CNN) -- The Federal Aviation Administration has issued additional "stop work orders" to construction and technology contractors after Congress failed to reauthorize funding for the federal agency.
Tuesday marked the fourth day of the partial FAA shutdown, which has forced thousands of employees from their jobs and halted dozens of major projects around the country.
Nearly 4,000 employees in 35 states, the District of Columbia and Puerto Rico have been furloughed, according to the FAA. Air traffic controllers will remain on the job.
"I am making a simple and straightforward request to Congress: Pass a clean FAA bill and immediately put thousands of FAA employees, construction workers, planners and engineers across America to work. In these tough economic times, we can ill afford to lay off hard-working Americans whose families depend on them," said Transportation Secretary Ray LaHood.
Efforts to continue funding hit a stumbling block over House Republican efforts to make it harder for airline and rail workers to unionize and over a move to cut subsidies for air service to rural airports.
Congress adjourned Friday without passing legislation, causing funding to end at midnight that night.
The FAA has said that contractors have been told to stop work on dozens of projects around the country, including a $43 million project in Las Vegas, Nevada, and a $31 million project in Oakland, California, to build new air traffic control towers.
More than $250 million in contracts to design and install runway status lights and nearly $20 million in construction and engineering contracts to strengthen air traffic towers in earthquake-prone areas have also been put on hold.
The furloughs have hit engineers, scientists, computer specialists, community planners and others.
Other effects of the lack of new legislation include the government not being able to collect about $200 million a week in airline taxes that normally go to the Airport and Airway Trust Fund, and shutdown of a $2.5 billion program providing grants for airport construction projects.