Sheldon Silver, the longtime speaker of the New York state Assembly, is expected to be arrested on corruption charges by federal authorities on Thursday after prosecutors subpoenaed records in a probe of undocumented payments he received from a law firm, sources said.

Silver, a Manhattan Democrat who has served as speaker for more than 20 years, is expected to be charged following an investigation sparked when Gov. Cuomo abruptly shut down an anticorruption commission he had created in 2013, sources said.

The specific details of the charges were not clear, but sources said that it was related to money Silver received from a small real-estate tax law firm.

The firm, Goldberg & Iryami PC, made the payments over about a decade, but Silver failed to list the income on his financial-disclosure forms, sources told The Post.

As speaker, Silver controls which legislation can be voted on, and has broad powers over the state budget.

Silver, 70, has been criticized by opponents for wielding too much power, and has been ensnared in controversy.

The FBI and prosecutors from Manhattan US Attorney Preet Bharara’s office began an investigation into the undisclosed money in December.

The prosecutors were looking into exactly what Silver did to earn the money, sources told The Post in December.

The probe came after an investigation by Cuomo’s Moreland Commission panel, which was looking into corruption in Albany when the governor shut it down.

One of the issues that the panel was looking into was how state lawmakers earn income from their non-government jobs.

Silver is a personal-injury lawyer associated with the high-profile law firm Weitz and Luxenberg.

Goldberg & Iryami specializes in an arcane form of law known as “tax certiorari,’’ according to the New York Times.

That involves challenging real-estate tax assessments and seeking reductions for developers who own residential or commercial property.

The firm appears to have only two lawyers, according to the Times.

The newspaper said, that since 2001, the firm and its principals have made six donations to Silver, totaling $7,600.

The most recent was in February, when it gave him $1,800, according to the report.

The Times added that the law firm has sought tax reductions for many properties on the Lower East Side, which is the area Silver represents.

In addition the financial controversies, Silver also became entangled in the Vito Lopez sex-harassment case when it became public that the speaker had hired two firms to defend the disgraced former assemblyman, spending nearly $700,000 in public funds.

Silver — who could not be reached for comment early Thursday — was nearly ousted as Assembly speaker by his fellow Democrats in 2000, when they unexpectedly challenged his leadership position. The coup failed.