President Biden is meeting with lawmakers on both sides of the aisle this week to discuss areas of bipartisan agreement on infrastructure spending, but Republicans continue to say tax increases as a “pay-for” are off the table.

Biden had meetings earlier in the week with House and Senate leadership and is meeting today with a half-dozen Senate Republicans who have been drafting the GOP alternative to the president’s sweeping $2.3 trillion infrastructure and jobs plan. The search for common ground is becoming more urgent as the White House has set a deadline of Memorial Day for “progress” on a package.

House Speaker Nancy Pelosi (D-CA), who was at the White House Wednesday with House Minority Leader Kevin McCarthy (R-CA), Senate Majority Leader Chuck Schumer (D-NY) and Senate Minority Leader Mitch McConnell (R-KY), said she was “more optimistic now that we will do [something] in a bipartisan way. But we’ll see.” After the meeting, Pelosi reiterated her plans to pass a bill by July 4.

Republican leaders have balked at the size of Biden’s infrastructure proposal and won’t stretch the traditional definition of infrastructure beyond roads, bridges and other physical improvements. After their meeting at the White House yesterday, McCarthy and McConnell also said raising the corporate tax rate is a non-starter.

“We’re not interested in reopening the 2017 tax bill. We both made that clear with the president. That’s our red line,” McConnell said.

Biden has said he is willing to negotiate on the size of the package and would consider raising the corporate tax rate to a number lower than the 28% he proposed. The president is also open to cutting a deal with Republicans on infrastructure and then moving his $1.8 trillion plan to expand access to education and child care in a separate, partisan bill.

Following the meeting with GOP and Democratic leaders yesterday, Biden said, “Generally, I am encouraged that there is room to have a compromise on a bipartisan bill that’s solid and significant and a means by which to pay for it without dropping all of the burden on middle-class and working-class people.”