Columbia, SC (WLTX, AP) - A government watchdog is trying to get legislators behind an effort to file a lawsuit against South Carolina's recently approved gas tax that raises money to fix the state's roads.

Ned Sloan of the South Carolina Public Interest Foundation has been sending letters to key lawmakers asking for them to file a parallel complaint to an earlier suit his group filed when the gas tax was proposed last year.

That case is still pending. He argues the law is unconstitutional.

Sloan wants lawmakers to ask the Supreme Court to look at the suit. One of the people Sloan contacted was Beaufort State Sen. Tom Davis, who's been a vocal critical of the gas tax.

Sloan sued the state multiple times over the years for what he believes are violations of the state constitution.

The gas tax passed earlier this month by the General Assembly raises the tax by 12 cents over six years to 28.75 cents per gallon. But it provides a way for South Carolina drivers to get the money back during the phase-in.

Gov. Henry McMaster vetoed the bill, but both chambers overwhelmingly voted to override that veto.

The Legislature hasn't increased any tax since 2010, when it overrode then Gov. Mark Sanford's veto for a 50-cent-per-pack cigarette tax hike.

The new tax goes into effect on July 1.