A union representing thousands of New York City prekindergarten teachers is laying the groundwork for a strike, casting a shadow on one of Mayor Bill de Blasio’s signature achievements as he explores a presidential bid.

Riding a wave of successful teacher protests across the country, District Council 1707 will begin voting Thursday on whether its 7,500 members in community-based organizations will walk out.

Chief among the union’s demands: a pay boost that would bring members’ paychecks in line with public school teachers’.

“They should be paid what they’re worth,” said Kim Medina, executive director of DC 1707. “They’re worth the money and should be respected as educators, and not glorified babysitters.”

Should a strike take place, it is likely weeks away and expected to be short-lived.

But the threat of an uprising in New York City comes at a politically delicate time for de Blasio, who is touting his education record in visits across the country as he tests the waters for a presidential run. His administration’s rapid expansion of universal pre-K is widely considered a chief accomplishment of his two-term tenure — one that is now being called into question by some of the teachers who helped make it happen.

Spokespeople for City Hall and the education department did not respond to requests for comment.

Two locals under DC 1707 will vote Thursday and Monday on whether to authorize a strike. Local 205 represents teachers in city-funded programs, while Local 95 includes members in Head Start programs, which are largely federally funded but also receive local money.

Union officials are aiming for a single-day action some time the first week of May. But a walk-out may not be necessary: Medina said the union hopes to work out its issues in a meeting with the mayor that is expected later this month.

Andrea Anthony, who represents the operators of community organizations as the executive director of the Day Care Council of New York, echoed that hope. She acknowledged it would be “difficult or impossible” for families to find care for their children during a strike, but noted that operators are “very concerned with the livelihood of those who care for our children in publicly funded child care programs.”

“It’s our hope to speak with the administration to discuss salary parity for all workers,” Anthony said.

At the center of the dispute is a long-standing issue: Teachers in community-run preschools make far less than their counterparts who work in schools run by the education department — though certification requirements are ultimately the same regardless of the setting.

The pay gap can be as much as 60 percent, which is particularly striking given that teachers in community settings are often women of color, while the majority of New York City public teachers are white.

The divide has been made more stark after the mayor rapidly expanded free pre-K. When de Blasio took office, only about 20,000 of the city’s 4-year-olds were served in free pre-K classes. Today, all children are guaranteed a seat, and 70,000 are enrolled.

To make room for so many students, the city is dependent on privately run centers —  many of them nonprofits — that serve about 60 percent of universal pre-K students. The rest are enrolled in schools and centers that are run by the education department.

Teachers employed in community centers have a starting salary around $42,000. Teachers employed by the education department are represented by the United Federation of Teachers, and salaries start around $59,000. Operators in community based organizations, or CBOs, say the gap has made it a struggle to recruit and retain teachers.

“The system [de Blasio] is creating is heavily reliant on CBOs,” said Jennifer March, executive director of the advocacy group Citizens Committee for Children of New York. “So if we want it to be stable, high quality, we need to get to parity.”

Medina and other advocates hoped there would be progress towards pay parity when the city released a new round of contracts for early childhood services. But those contracts are now out — without the increased funding that advocates hoped for.

“The city doesn’t want to pay us, and the mayor wants to tout how we have all these wonderful programs that bring us early education,” Medina said. “But it’s the CBOs that brought this to the table.”