House Intelligence Committee Chairman Rep. Devin Nunes has signed off on subpoenas to the firm behind the Trump dossier, after he recused himself from the Russia investigation -- and without telling Democrats, sources tell CBS News.

A Republican aide tells CBS News Nunes signed the subpoenas addressed to Fusion GPS — the firm that produced the questionable dossier of memos on alleged information on Donald Trump's ties to Russia — at the request of Rep. Mike Conaway (R-Texas). Nunes, a California Republican, delegated his responsibilities in the committee's investigation of Russian election meddling to Conaway earlier this year. The aide tells CBS News that Nunes only signed the subpoenas, in compliance with the committee's rules.

But Nunes left Democrats in the dark about the subpoenas, according to a Democratic committee source and a person familiar with the matter. The subpoenas, according to the Democratic committee source, were issued unilaterally by the majority, without the minority's agreement and despite the good-faith engagement so far by the witnesses on cooperation terms.

At the moment, it is unclear what the subpoenas demand.

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Nunes recused himself from the committee's investigation after the Office of Congressional Ethics in April confirmed it is investigating allegations that Nunes might have made unauthorized disclosures of classified information.

Fusion GPS' co-founder, Glenn Simpson, has already appeared privately before the Senate Judiciary Committee for a transcribed interview. Republican leaders of the House Intelligence Committee and Senate Judiciary Committee have made investigating Fusion GPS a key component of Russia-related inquiries.

CBS News' Catherine Reynolds and Walt Cronkite contributed to this report.