Senate Republicans are warning companies that cut off donations to the GOP after the U.S. Capitol attack that their standing on the Hill may suffer if they don't now speak out about Democrats' efforts to overturn a Republican House victory in Iowa.

Why it matters: Democrats are trying to expand their narrow margin in the chamber, a vital consideration heading into midterm elections, in which the party in power historically loses roughly two dozen seats.

• Senate Minority Leader Mitch McConnell is leading a group that is warning of repercussions if some big-name companies don't follow the precedent they set when they cut ties with Republicans who voted to block certification of President Biden's Electoral College victory.

What's new: That thinly veiled threat will be relayed in a letter co-authored by McConnell, Sen. Tom Cotton (R-Ark.), Sen. Chuck Grassley (R-Iowa), and Sen. Joni Ernst (R-Iowa).

• None voted against the election certification.
• "We are asking you to apply the same standard to this attempt to overturn an election that you applied to the Republicans who objected to certain states' electoral votes," the senators write.
• "If you decide to not speak out about this brazen attempt to steal an election, some may question the sincerity of your earlier statements and draw the conclusion that your actions were partisan instead of principled."

The backstory: Iowa officials certified Republican Rep. Mariannette Miller Meeks' razor-thin victory in late November.

• She beat Democrat Rita Hart by just six votes after a recount. But Hart has appealed to the House Administration Committee, asking it to conduct its own investigation into ballots her campaign insists should have been counted.
• The process could trigger a vote by the full House over who will represent the seat.
• Republicans say Democrats' efforts to relitigate the election closely mirrors GOP objections to Biden's close victories in key states last year.

What they're saying: "If the businesses who condemned Republicans in January don’t condemn Democrats for doing the same, everyone will question whether these companies are truly committed to free elections," Cotton said in a statement on the letter.

• McConnell called the prospect of a House vote on the seat "absurd" and said Democrats "want to use brute political power to overturn a democratic result because they lost."

Between the lines: This week's letter will be released as an open appeal to corporate America. But a source close to Cotton said they plan to directly press government relations staff for 15 companies that were particularly forceful in their condemnations of electoral college objectors.

• The companies on the list include Fortune 100 firms with regular business before Congress, including Amazon, Verizon, Mastercard, Dow, Nike and Walt Disney.
• The message, the source close to Cotton said is "there will be consequences if you start acting like partisan Democrats. ... That would probably change how members interact with these organizations in a number of ways."

Be smart: The language of the letter itself was less ominous than that warning, offered only on the condition of anonymity.

• But the letter's implication is clear enough: speak up as you did in January or risk making permanent political enemies.

The bottom line: McConnell's decision to sign on to the letter is sure to get the attention of the companies receiving it.

• The source close to Cotton said Republican lobbyists for some of those companies have privately said they "agree on the merits" but have declined to say anything publicly.