WASHINGTON (Reuters) - Facebook Inc Chief Executive Officer Mark Zuckerberg will hold meetings with some U.S. lawmakers on Monday, a day before he is due to appear at Congressional hearings over a political consultancy’s use of customer data, two congressional aides said on Sunday.

The planned meetings at Capitol Hill are expected to continue through Monday afternoon and include some lawmakers from committees before whom Zuckerberg is due to testify, said the aides, who asked not to be identified because the meetings have not been made public.

Facebook declined to comment.

Zuckerberg is scheduled to appear before a joint hearing of the U.S. Senate Judiciary and Commerce committees on Tuesday and the U.S. House Energy and Commerce Committee on Wednesday.

Facebook has come under fire in recent weeks after it said that the personal information of up to 87 million users, mostly in the United States, may have been improperly shared with political consultancy Cambridge Analytica.

A Facebook spokesman said on Sunday that the company plans to begin telling affected users on Monday.

London-based Cambridge Analytica, which has counted U.S. President Donald Trump’s 2016 campaign among its clients, has disputed Facebook’s estimate of the number of affected users.

Zuckerberg is expected in his testimony to recognize a need to take responsibility and acknowledge an initial failure to understand how many people were affected, a person briefed on the matter, who asked for anonymity, said on Sunday.

Zuckerberg said in a conference call with reporters last week that he accepted blame for the data leak, which has angered users, advertisers and lawmakers, while also saying he was still the right person to head the company he founded.

On Friday, Facebook backed proposed legislation requiring social media sites to disclose the identities of buyers of online political campaign ads and introduced a new verification process for people buying “issue” ads.

The steps are designed to deter the kind of election meddling and online information warfare that U.S. authorities have accused Russia of pursuing, Zuckerberg said on Friday. Moscow has denied the allegations.

In February, U.S. Special Counsel Robert Mueller charged 13 Russians and three Russian companies with interfering in the 2016 U.S. presidential election by sowing discord on social media.

Zuckerberg, on the call with reporters, said Facebook should have done more to audit and oversee third-party app developers like the one hired by Cambridge Analytica in 2014.