President Donald Trump's lawyer has received requests for information from two congressional panels investigating alleged Russian political meddling.
Michael Cohen confirmed to US media that he had been asked to "provide information and testimony" about any contacts he had with the Kremlin.
Mr Cohen said he turned down the request because it was "overly broad" and "not capable of being answered".
Last week Mr Trump's son-in-law Jared Kushner was named in the Russia probe.
Mr Cohen is the latest Trump associate to rebuff the House and Senate investigations into the matter.
"I declined the invitation to participate, as the request was poorly phrased, overly broad and not capable of being answered," he told ABC News.
He later told CNN that lawmakers "have yet to produce one single piece of credible evidence that would corroborate the Russia narrative".
The widening inquiry into Russia's alleged interference in the US election and whether Trump campaign officials colluded with the Kremlin is threatening to engulf his fledgling presidency.
His son-in-law is said to be under scrutiny as part of the FBI inquiry.
According to US media, Mr Kushner, a top White House aide, discussed setting up a back channel line of communication with Moscow's envoy to Washington during a December meeting.
In Tuesday's daily briefing, White House Press Secretary Sean Spicer refused to be drawn on whether Mr Kushner had tried to set up such a secretive mode of contact.
Mr Spicer said the claims were based on reports "not substantiated by anything but anonymous sources".
The press secretary added, however, that "in general terms, back channels are an appropriate part of diplomacy".
Meanwhile, former National Security Adviser Michael Flynn is to submit documents to the Senate intelligence committee as part of its investigation, government sources tell US media.
Last week, Mr Flynn initially said through his lawyer that he would refuse to hand over files relating to his contacts with Russians dating back to June 2015.
Similar congressional request for information have been sent to other former Trump aides, including Roger Stone, Paul Manafort and Carter Page.
Mr Manafort and Mr Stone have complied, but Mr Page is not thought to have responded yet.