CHICAGO (CBS) — Some stations on the Metra Electric Line and South Shore Line could be shut down during the upcoming NATO summit, and passengers at other stations could face airport-style security screenings, due to the Secret Service security plan that could be released as soon as Friday afternoon.

CBS 2 Chief Correspondent Jay Levine has exclusive details on those security measures, which the Secret Service is expected to officially unveil on Friday, or at the very latest, on Monday. Federal officials have promised the announcement will include a “comprehensive list of street closures and parking restrictions surrounding the NATO summit.”

The Secret Service has been battling with Metra and the Northern Indiana Commuter Transportation District over the security measures that will be needed on the Electric and South Shore lines, which both run directly under McCormick Place.

Metra and NICTD won round one of that battle, as trains on those two lines will continue to operate during the summit, although there will be significant delays at times, with trains possibly being stopped for security screening before passing McCormick Place.

The commuter rail agencies are still in talks with the Secret Service over major security measures for passengers, including airport-style screening of all riders during the summit. That would mean commuters on those lines would face patdowns, X-ray screenings, and long security lines at their stations before boarding trains.

The Secret Service initially wanted all trains to stop short of McCormick Place, with shuttle buses taking passengers around the summit site.

Then they talked about canine units conducting searches on trains, which would be halted before reaching McCormick Place.

Now, the Secret Service is planning for airport-style security screening at a limited number of stations on those two train lines. Many other stations on the Electric and South Shore lines – serving the South Side, southern suburbs and northwest Indiana – would be shut down during the summit.

Neither Metra nor the Secret Service will talk about the security measures yet. But sources said, with just over two weeks until the summit, nothing has been decided.

Earlier this week, Chicago police handled hundreds of May Day demonstrators marching from the West Side into the Loop, successfully containing the crowd with no arrests or injuries.

Many called it a trial run or dress rehearsal for NATO – for both police and protesters.

What most people didn’t see were all the CTA buses quietly re-routed around the demonstrations and marches, which will also be part of a CTA strategy to be announced after the Secret Service restrictions released.

The CTA plan will encourage commuters to use its rail lines, all of which will operate with full service. Many of its buses will not.

There will be what the CTA calls “hard closures” of bus routes affected by the security perimeter; and “soft rolling closures,” or temporary delays on other bus lines – like there were during Tuesday’s protest march – to wait for passing motorcades, parades, or demonstrations.

The CTA said bus managers and volunteers will be on the street at bus stops to help riders cope with the three-day detours.

What we’re hearing is that the CTA, RTA, and most other local agencies have been told to wait for the Secret Service announcement, before revealing their own plans.

That hints at an avalanche of information coming out about summit plans right after the feds break their silence and post all the security restrictions on various websites.

The tentative plan had that happening at around 6 p.m. Friday, but that could change.

–CBS 2 Political Producer Ed Marshall contributed to this report.