Senate Republican negotiators on Thursday rolled out a massive business assistance package, seeking to stave off a recession and soaring unemployment because of the coronavirus crisis.

The centerpiece of the plan are rebate checks of $1,200 for individuals and $2,400 for married couples and a 90-day extension of the April 15 tax filing deadline, but it also includes a slew of business tax breaks that received little public discussion in recent days.

The strong tilt toward helping businesses is certain to run into strong objections from Senate Democratic Leader Charles Schumer (N.Y.) who says the stimulus should focus on revamping the nation's health care system and workers directly affected by an economic downturn.

Senate Majority Leader Mitch McConnell (R-Ky.) praised the bill, which he introduced on the Senate floor, for taking "bold action" and invited Democrats to begin negotiating immediately.

The proposal doesn't include a price tag but GOP lawmakers emerging from a meeting Thursday estimated it would cost around $1 trillion.

It would defer the payment of employer-side payroll taxes until 2021 and 2022, with half of payroll taxes for 2020 due by Dec. 31, 2021, and the other half due by Dec. 31, 2022.

The long delay in payments effectively grants President Trump the payroll tax holiday he requested for this year at a meeting with Republican senators last week. GOP senators initially balked at the proposal but this provision allows them to split the difference with the president.

Trump last week proposed zeroing out the payroll tax for employers and employees through the election but Republican senators balked at the cost.

The GOP authors of the plan argue this measure will provide "critical cash flow and liquidity" to deal with the coronavirus crisis.

"We are going to increase the limit on interest deductibility. We'll speed up the recovery of Alternative Minimum Tax credits. And we'll relax limitations on how companies use losses from previous years to reduce their tax burdens," Senate Finance Committee Chairman Chuck Grassley (R-Iowa), who oversaw the drafting of the tax provisions, said on the Senate floor.

Democrats quickly took issue with the GOP plan. Sen. Ron Wyden (Ore.), the top Democrat on the Finance Committee, said "Republicans seem to be prioritizing the corporate tax wish list over the economic well-being of people who are losing their livelihoods at this very moment."

The plan also eases limits in Republicans' 2017 tax-cut law on carrying back net operating losses (NOLs) and deducting business interest. Prior to the 2017 tax law, businesses could carry losses back up to two years, but the GOP tax law did away with NOL carrybacks. The plan released Thursday would allow losses from 2018, 2019 and 2020 to be carried back for five years, in an effort to provide businesses with more cash flow.

It also makes some technical corrections to the 2017 tax law, including a fix that will allow retailers and restaurants to be able to write off the full costs of their renovations in the year that they were made, rather than over 39 years.

The package includes a separate chapter drafted by Sens. John Thune (R-S.D.), Richard Shelby (R-Ala.) and Roger Wicker (R-Miss.) that would provide more than $200 billion in collateralized loans for the airline industry and other industries hit hard by health quarantines.

It would provide $50 billion for passenger airlines, $8 billion for cargo air carriers and up to $150 billion for other "eligible entities."

The aid is set aside for companies "that have incurred losses as a direct result of the coronavirus global pandemic" to stay in business. Treasury Secretary Steven Mnuchin would determine whether a company's "continued operations" have been jeopardized by the pandemic.

The proposal explicitly bars the Treasury secretary from making direct cash grants to airlines and other industries after Republicans pushed back hard against an airline bailout in a meeting with Mnuchin on Thursday. It would, however, suspend certain aviation taxes through the end of the year.

The measure also includes language barring the use of federal loan money to compensate senior executives - at least for a period of two years after the legislation's enactment.

Another major component is a $300 billion relief package for small businesses spearheaded by Senate Small Business Committee Chairman Marco Rubio (R-Fla.).

It would provide loans with 100 percent federal guarantees to small employers who keep their workers on payroll during the crisis. If small business owners avoid laying off workers, the loans would be 100 percent forgiven.

The loans would be permitted to cover payroll expenses, sick leave, supply chain disruptions, mortgage payments and other debts. It includes $240 million in grants for small business development centers and women's business centers for counseling and training.

Senate Health, Education, Labor and Pensions Committee Chairman Lamar Alexander (R-Tenn.) and Sen. Susan Collins (R-Maine), who faces a tough election this year, worked with Rubio on the language.

The rebate check amounts would increase by $500 for each child in a household. The amounts would start phasing out for individuals who made more than $75,000 in 2018 and married couples who made more than $150,000, and would be fully phased out for individuals who made more than $99,000 in 2018 and married couples who made more than $198,000. Those with little-to-no tax liability but at least $2,500 of income would get a minimum of $600.

Tax experts across the ideological spectrum criticized the design of the rebate checks, because the amount of the rebate phases in at the low end of the income spectrum.

The direct payments, while generous, are still less than what the Trump administration requested. The Treasury Department earlier in the week floated a proposal of two $1,000 checks per eligible individual, which would have cost an estimated $500 billion.

GOP lawmakers estimated their reduced rebate-check proposal would cost closer to $300 billion.

The extension of the filing deadline is a priority for many lawmakers and tax preparers.

The Treasury Department announced earlier this week that it is extending the payment due date from April 15 to July 15, and lawmakers and accountants think the filing and payment deadlines should be the same.

The GOP senators are also proposing to allow estimated tax payments for individuals and corporations that are due after the date of enactment to be postponed to Oct. 15.

Senate Republicans' plan includes tax incentives to encourage charitable giving, including a provision that will allow individuals to deduct up to $300 of donations to nonprofits in 2020 even if they don't itemize their deductions.

A group of prominent charities, such as the American Red Cross and United Way, had urged lawmakers in a letter Wednesday to include a universal charitable deduction, expressing concerns that they will see a decline in donations in light of the pandemic.

The health care-focused chapter of the bill includes 43 provisions drafted by the Senate Health and Finance Committees to help contain the coronavirus.

Some of the provisions would direct the national academies to recommend way for strengthening the supply chain for drugs and medical devices, provide liability protection for the manufacturers of personal respiratory equipment, allow the Strategic National Stockpile to stockpile medical supplies, and the Food and Drug Administration to prioritize the review of drug applications.

Finance Committee-drafted provisions would allow patients to use health savings accounts to purchase medical products needed for self-quarantining and social distancing as well as provide economic assistance to health care providers by suspending the so-called Medicare sequester, a budget reform of the past designed to reduce Medicare costs.