House Democrats plan to vote as soon as Friday on their $1.9 trillion coronavirus relief bill, a key initial hurdle as they race to renew federal unemployment benefits, provide stimulus checks to millions of Americans and inject billions of dollars to speed the administration of COVID-19 vaccinations.

The bill is expected to win narrow House approval this week, then go to the Senate, where its fate is less certain. The legislation faces a complicated procedural gauntlet in the Senate that threatens key provisions, such as increasing the minimum wage nationally to $15 per hour.

Democrats are using a procedural tool called budget reconciliation to pass their COVID-19 package. That process prevents any Republican senator from filibustering the bill and allows Democrats to approve it without GOP votes. But Democrats’ Senate majority is razor thin, as both Democrats and Republicans each have 50 seats – only Vice President Harris’ tie-breaking vote gives Democrats the majority.

That means the party has no room for error. Just one Democrat who objects to one aspect of the bill could sink the entire legislation. Or if a key provision is knocked out because of procedural objections, that could upset the fragile consensus Democrats are striving to achieve.

Pandemic aid is a top priority for President Joe Biden in his first 100 days in office. Congressional Democrats have the votes and should be able to enact the relief bill – it would be politically calamitous if they didn’t – but the legislative process in the coming weeks is likely to be perilous.

Republicans support some provisions of the legislation, but GOP lawmakers say too little aid is targeted to vaccine distribution – less than 1% of the bill’s total cost. They also say the bill is chock full of non-pandemic Democratic priorities, such as increasing the minimum wage and allocating $350 billion to state and local governments.

House Republican Whip Steve Scalise of Louisiana says there’s more than $1 trillion in previously enacted aid that hasn’t been distributed and that Washington should allocate those funds before adding nearly $2 trillion to the $28 trillion national debt.

Overall, the Democrats’ sweeping legislation seeks to address both the public health crisis and the economic crisis triggered by the pandemic. It would include another round of checks – $1,400 for each eligible person earning less than $75,000 annually. Those checks, which would be in addition to the $600 direct payments that Congress approved in December, would cost $422 billion.

The aid plan would target $160 billion to combat the coronavirus, including funding for vaccines, testing and tracing. It also would increase federal housing and nutrition assistance, boost access to childcare, and incentivize states to expand their Medicaid programs.

The current $300 weekly federal unemployment benefit going to 10 million Americans – which expires March 14 – would be increased to $400 under the bill and run through the end of August. That federal benefit, which would be in addition to weekly state-based unemployment aid, would cost $246 billion.

The bill includes $130 billion for K-12 schools, including scaling up testing and tracing and boosting personal protective equipment for classrooms.