Read the whole article but here are a few tidbits:

Mayor Bill de Blasio…has embraced the United Federation of Teachers and its president, Michael Mulgrew, meeting more with him over the past two years than with any other registered lobbyist, city records show. The men usually chat weekly and sometimes daily. The mayor has become a regular at union parties, lunches and other events.

And,

With regular phone calls and sit-downs, Messrs. de Blasio and Mulgrew also wage parallel and sometimes coordinated battles against the growth of charter schools, which had flourished under Mr. Bloomberg.

And,

More often, though, the men have been on the same page—and right from the beginning of Mr. de Blasio’s term. The teachers union was the first municipal union to get a new contract in early 2014. Mr. de Blasio met for lunch on March 9 of that year with Mr. Mulgrew and Randi Weingarten, who heads the American Federation of Teachers, the union’s umbrella group. 

On April 9, the national teachers union gave $350,000 to the Campaign for One New York, an organization that promotes Mr. de Blasio’s broader agenda. Three weeks later, the nine-year contract was announced.

And,

Charter advocates point out that many of their schools outperform traditional public schools and say Mr. de Blasio is largely opposed to charter schools because of his relationship with the big union.