Top medical groups are voicing their opposition to the decision to include a repeal of ObamaCare’s individual insurance mandate in the Senate version of the GOP tax-reform bill.

"We join together to urge Congress to maintain the individual mandate," the group, which includes Blue Cross Blue Shield Association, American Hospital Association, and American Academy of Family Physicians, wrote in a letter on Tuesday.

"There will be serious consequences if Congress simply repeals the mandate while leaving the insurance reforms in place: millions more will be uninsured or face higher premiums, challenging their ability to access the care they need," they wrote.

The letter was addressed to Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.), Senate Minority Leader Charles Schumer Chuck SchumerVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year Pelosi orders Capitol flags at half-staff to honor Ginsburg MORE (D-N.Y.), Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) and House Minority Leader Nancy Pelosi Nancy PelosiSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Trump is betting big on the suburbs, but his strategy is failing 'bigly' Trump orders flags at half-staff to honor 'trailblazer' Ginsburg MORE (D-Calif.).

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The letter comes after Senate Republicans heeded President Trump's demand to include the repeal of the mandate in the tax-reform bill.

While the move could drive centrists in Congress away from supporting the plan, repealing the mandate gives Republicans more money to offset the cost of tax cuts, and would fulfill a the seven-year Republican campaign promise to eliminate a core part of former President Obama’s signature health-care law.

Senate Republicans, as well as the White House, are hoping to achieve their first legislative victory since Trump took office in January.

Republicans in the upper chamber attracted the ire of the White House and their counterparts in the House when they failed to repeal and replace ObamaCare multiple times earlier this year.