By Courtney Sherwood

PORTLAND Ore. (Reuters) - A U.S. congressman asked the White House on Friday to investigate possible campaign finance law violations over allegations that an anti-marijuana group's upcoming Oregon "education tour" was partly financed by federal money in the run-up to a statewide vote on pot legalization.

Oregon Democrat Earl Blumenauer called the week-long Oregon Marijuana Education Tour a "smokescreen" for opponents seeking to defeat a November state ballot measure that if passed would legalize recreational pot use by adults in the state.

Washington state and Colorado this year became the first two U.S. states to permit recreational sales of marijuana, and voters in Alaska and the District of Columbia will join Oregon in voting on similar legalization initiatives this fall.

"The bias of the speakers selected, the overall one-sided focus of the events and the proximity between these events and the upcoming election are cause for concern," Blumenauer wrote in his letter to the White House Office of National Drug Control Policy.

Blumenauer, a proponent of marijuana legalization, said federal money has been used to pay for promotional advertising and for salaries of county officials organizing the tour, even after state leaders warned that doing so would constitute a political act in violation of campaign finance laws.

Recent polling indicates that Oregon's marijuana legalization ballot measure, which would legalize pot for adults 21 and older and tax its sales, is slightly favored to pass, though a similar effort failed two years ago.

In June, SurveyUSA found 51 percent supported the measure to 41 percent opposed, with a margin of error of 4.2 percentage points. Fifty-four percent of voters polled in April and May by DHM Research supported marijuana legalization to 38 percent opposed, with a 4.9 percentage-point margin of error.

The Oregonian newspaper reported that Clatsop County District Attorney Joshua Marquis, who has acted as a spokesman for legalization opponents, said Blumenauer's allegations amounted to "political thuggery" and that tour sponsors banned discussion of the ballot initiative at their events.

The tour, slated for Oct. 1-7, is headlined by prominent anti-marijuana activist Kevin Sabet and features officials affiliated with the campaign to defeat the ballot measure. At least one nonprofit has backed away from the tour in response to the allegations.

(Reporting by Courtney Sherwood; Editing by Eric M. Johnson and Eric Beech)