Washington (CNN) A feud between two California lawmakers spilled into the public recently, with one alleging conspiracy and the other threatening legal action.

Democratic Rep. Ted Lieu in December accused Republican Rep. Devin Nunes of conspiring with Lev Parnas, an associate of President Donald Trump's personal lawyer Rudy Giuliani and a key figure in the Ukraine scandal at the center of Trump's impeachment, to undermine the US government. A lawyer for Nunes, the top Republican on the House Intelligence Committee, then threatened legal action if Lieu doesn't apologize.

On Friday, Lieu tweeted the first page of a December 31 letter from Nunes' attorney, Steven Biss, threatening to sue to protect his client's reputation.

Lieu included his curt response: "I welcome any lawsuit from your client and look forward to taking discovery of Congressman Nunes," Lieu wrote in a reply letter dated January 16. "Or, you can take your letter and shove it."

Attached is the first page of a five page letter in which the lawyer for @DevinNunes threatens that Rep Nunes will sue me. Attached is my response. pic.twitter.com/bWAqdRhq97

CNN has reached out to Biss and Nunes' office for comment.

In his letter to Lieu obtained by CNN, Biss included an email from Lieu that asked recipients to sign a petition calling for Nunes' removal from the House Intelligence Committee.

Biss called the California Democrat's actions "unlawful and grossly unethical."

"Your poisonous lack of civility infects, corrodes and degrades American society. It is needless and pointless, and it threatens to impair the important business of Congress," the letter reads.

Biss also demands Lieu to send an email retraction, post the retraction on Twitter, and "cease and desist from the publication of any further false and defamatory statements."

The letter also says that Nunes intends to request an ethics investigation and review if Lieu refuses to take action.

Lieu's office said he had no further comment at this time beyond his response letter.

In his tweeted response, Lieu pointed to Parnas' Wednesday interview with MSNBC in which he said he recalled speaking and meeting with Nunes , but also said the pair doesn't "have too much of a relationship." Phone records released last month by Democrats as part of the impeachment inquiry showed that Nunes had exchanged multiple phone calls, at key moments, with Parnas.

Parnas, a Soviet-born businessman, was indicted in October by New York federal prosecutors on campaign finance charges. He has pleaded not guilty to the charges.

Nunes confirmed to Fox News on Wednesday that he had spoken with Parnas, after previously saying such a conversation would have been "very unlikely."

Democrats say Trump abused his office by directing a pressure campaign for Ukraine to announce an investigation into former Vice President Joe Biden in exchange for $400 million in US security aid and a White House meeting. Trump, Democrats say, then stonewalled congressional investigators to coverup the misconduct.