Commuters who ride the 4,5 or 6 lines are in for a major disruption for some must-do repair work come Monday.

“The switches between the southbound local and express tracks north of 14 St-Union Sq are at the end of their useful lives—they were last replaced more than 20 years ago. Reliable switches are critical to keeping trains running on time—and allow us to move around stopped trains if there is an unforeseen disruption—like a customer needing medical attention. So, we’re replacing them,” the MTA said on its website.

The MTA described the job as “intense work,” which requires the removal of track and track beds.

Commuters near the 14 Street Station at Union Square will be impacted by a slow speed order, which should last through the end of the month. The MTA says there will be noticeable changes during rush hour.

In addition to the slower speeds, some 5 trains will be rerouted long the 2 line to avoid congestion, according to the MTA.

Overnight and on weekends, parts of service to the 4, 5 and 6 lines will be suspended. Service on these lines between Grand Central-42 St and Brooklyn will wrap at 9:30 p.m. nightly and not be running on Saturdays or Sundays.

The MTA will also utilize this unlimited access to the track beds to complete other repairs, such as track replacement at Canal Street and near Borough Hall, rail grinding in multiple locations and structural repair work.

“Our fiscal crisis and the COVID-19 pandemic are real challenges, but they’re not going to stop us from performing this critical project to improve the reliability, performance and safety of our system for     riders in Brooklyn, the Bronx and Manhattan,” said NYC Transit Interim President Sarah Feinberg in a press release. “We’re working to make sure this work causes as few disruptions as possible for our customers and look forward to getting this vital project started.”