A bus strike affecting more than 20,000 students in Nassau County is stretching into a fourth day Thursday as some school officials look to other transportation companies to fill the gap.

The Rockville Centre school district already hired another bus company — Oceanside-based Guardian Bus Co. — for drop-offs and pickups of students at its seven schools.

Outside Floyd B. Watson Elementary School on Wednesday afternoon, about 15 students boarded a Guardian bus.

“Transportation is a major issue,” principal Joan Waldman said. “They’re very young, and if you need a bus there aren’t nearly as many options if the parents aren’t available.”

In addition to Rockville Centre, the labor dispute meant students in the Baldwin, Freeport and Hicksville systems remained without their regular rides to and from schools Wednesday on Baumann & Sons Buses’ vehicles.

Negotiations overseen by a federal mediator are scheduled to resume Friday morning between the Ronkonkoma-based firm and Transport Workers Union Local 252, which represents nearly 400 drivers, monitors and mechanics. The parties negotiated until 2:30 a.m. Wednesday without reaching a settlement.

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“They need to fix this,” said Alexis Smith, who accompanied her 9-year-old son to Leo F. Giblyn School in Freeport on Wednesday morning. “I’m a police officer — NYPD — so I’ve got to rush to work.”

School bus strikes are rare on Long Island. This job action, which started at 5 a.m. Monday, is the longest on the Island in years.

The last such strike in Newsday’s records was in September 2003, when 200 drivers and bus monitors who were members of TWU Local 252 went on strike against Laidlaw Transit Inc.’s Center Moriches terminal.

That strike, which began on the first day of school, affected about 12,000 students in eastern Suffolk County. It lasted three days until the parties resumed negotiations and reached an agreement.

In the current situation, the parties have been at loggerheads over wage increases and payment to drivers on days off in the school calendar, as well as what is called “charter pay.” Drivers want more wages for field trips during the school day, TWU Local 252 president Debra Hagan said.

Company president Ronald Baumann said in a statement that the company is “committed to continuing negotiations in good faith to resolve the issue for the benefit of all affected.”

In Freeport on Wednesday morning, the flow of cars, vans and taxis outside the Giblyn school grew steadily between 8 and 9 a.m. as parents and grandparents dropped off students, then sped on to jobs and errands.

“I’ve gotta call in now and tell them I’m going to be late,” said Jeff Mofenson, who manages a fast-food restaurant but spent a half-hour Wednesday negotiating heavy neighborhood traffic to take his first-grader to school.

School staffers in windbreakers stood outside in 48-degree weather directing the vehicle flow and answering parents’ questions in a mixture of English and Spanish. Like other schools hit by the bus strike, Giblyn expanded its schedule to a 7 a.m. opening and a 5 p.m. closing to allow more time for drop-offs and pickups.

“It is running smoothly,” Freeport schools Superintendent Kishore Kuncham said as he observed drop-offs at Giblyn. Kuncham, nonetheless, voiced frustration with the pace of strike negotiations, as did many parents.

Some of the strike’s effects were lighter on Tuesday, when most public schools did not hold classes because of Election Day. Friday also will see a lesser impact, because three of the four affected districts are closed in observance of Veterans Day, which is Saturday.

The job action also has affected students in private schools who are transported on buses by the local districts.

Before this week’s strike, the most recent similar labor dispute was two years ago and also involved Baumann & Sons Buses.

At that time, members of Teamsters Local 1205 who worked for Baumann and its affiliate, Acme Bus Corp., threatened to strike in September and October 2015. A work stoppage, which would have affected 35 districts in Nassau and Suffolk counties, was averted when a contract agreement was reached.