A new poll from Gallup found Republicans' tax law to still be unpopular.

Thirty-nine percent of people surveyed by Gallup approved of the law, while 52% disapproved.

A NBC News/Wall Street Journal found that 27% of people thought the tax law was a good idea, and 36% said it was a bad idea.

The surveys are the latest in a string of polls that have shown the law to have dismal popularity.

The numbers could be worrying for Republicans, who are relying on tax cuts to be a large part of their 2018 midterm election message.

A pair of new polls suggests Americans still aren't on board with the new Republican tax law, and its unpopularity could be a problem for the GOP in this year's midterm elections.

Just 39% of Americans in a new survey from Gallup said they supported the new tax law, while 52% disapproved of the law. That represents a slight improvement from Gallup's survey immediately after the law's passage in January, when just 33% of respondents supported it.

But the law remains significantly underwater, and many people aren't sure how it will affect their income.

According to Gallup:

9% of people surveyed said they expected their taxes to increase under the new law;

18% expected their tax burden to decrease;

17% said they expected their taxes to stay the same;

56% said they weren't sure.

According to the Tax Policy Center, 65% of Americans should see a tax cut of more than $100 in 2018, while 6% should see an increase of $100 or more.

Also on Monday, NBC News and the Wall Street Journal released their own poll showing the law is unpopular. Just 27% of people told NBC/WSJ that the law was a good idea, while 36% said it was a bad idea. Thirty-four percent of people did not have an opinion.

The polls are another in a line of recent data hinting at the law's political implications. For instance, most Americans have not noticed a larger paycheck since the law was enacted. According to a CNBC poll released in March, just 32% of people reported an increase in take-home pay since the law was implemented in January.

The law's unpopularity is particularly worrying for Republicans, since the issue is expected to be the centerpiece of the party's 2018 midterm messaging.

For instance, the GOP-linked American Action Network has spent about $30 million in ads focusing on the tax law since August and is running $1 million worth of ads this month in vulnerable GOP districts.

The law also did little to help sway the special election in Pennsylvania, which was won last month by a Democrat, Conor Lamb, even though President Donald Trump carried the district by almost 20 points in 2016. Republican spending on ads that focused on the law dived in the weeks leading up to the vote, and Lamb hammered the GOP by saying the law favored the rich.