House and Senate negotiators on Wednesday finalized a deal to combat heroin and prescription drug abuse, but the bill’s chances of clearing Congress could be complicated by Democrats who argue it does not include enough funding.

The bill is popular with members in both parties and several lawmakers in tough re-election contests are eager to promote it back home as evidence they are getting things done in Washington.

But Democrats have long pushed for the additional funding arguing that without it the bill will not deliver on its promise to help stem the growing abuse of opioids across the country.

“We are debating a bill to address the opioid epidemic. It should include the funding necessary to actually fight that epidemic,” said Sen. Patty Murray (D-Wash.), a member of the conference committee that drafted the bill. She offered one of two amendments Wednesday that would have increased funding for the bill’s programs. Both failed along party lines.

Democrats have been trying to include additional spending in opioid legislation for months, but they lost a bid to add $600 million to the Senate’s bill earlier this year, after only five Republicans joined them to vote for the additional funds.

Leading Republicans argue funding has already increased significantly and lawmakers can attempt to find more money later this year when the annual spending bills are finalized.

“I cannot think of other provisions of the budget where we’re spending seven times what we did two years ago,” said Sen. Lamar Alexander (R-Tenn.), chairman of the Senate’s Health, Education Labor and Pensions committee, who was also part of the group negotiating the opioid bill.

“I’m opposed to the amendment, but I’m in favor of the policy,” Alexander explained. “And I’m in favor of funding, this is just not the way to do it, and we can get it done in an appropriate way soon.”

Democrats are wary of kicking the can down the road.

“We can’t do it on the cheap,” said Senate Minority Leader Harry Reid (D-Nev.). “That’s what they’re trying to do.”

But leaders would not say whether that meant Democratic senators would withhold the needed votes for the bill when it comes to the floor.

Earlier this year, after Democratic senators lost out on their bid to add $600 million of additional funding, they still voted for the opioid bill, which passed the Senate on a 94 to 1 vote.

The conference agreement is expected to easily pass the House.

Both House and Senate leaders are expected to hold votes on the conference report before the end of next week, when Congress goes into an extended recess to accommodate the political conventions and the summer campaign season.

“We’ll be voting before we go to the convention,” Senate Majority Leader Mitch McConnell (R-Ky.) said. “And hopefully our Democratic friends in the Senate will vote the same way they did the first time, when the bill went through the Senate.”