AUGUSTA, Maine — Citing potential constitutional issues, Gov. Paul LePage on Tuesday vetoed a bill that would have prohibited the Maine Department of Conservation from employing foreign laborers at logging operations on state-owned land.

The Maine Bureau of Parks and Lands, which is part of the Department of Conservation, already has a policy barring contractors from using “bonded” workers — federally approved foreign laborers typically from Canada — on logging jobs within state parks or public lands.

But Sen. Troy Jackson, D-Allagash, introduced LD 340 to write the prohibition into statute after he documented an instance of a Canadian logger working on a public lot in northern Maine earlier this year.

Jackson, a logger himself, and others have accused landowners and contractors of skirting or violating federal and state laws by hiring lower-cost Canadian loggers while Maine workers struggle to find jobs.

In his letter to lawmakers, LePage wrote that he was vetoing the bill on constitutional grounds. He also referenced the fact that his predecessor, Democratic Gov. John Baldacci, vetoed a similar bill in 2003.

“This veto has nothing to do with the policy in this bill,” LePage wrote. “Governor Baldacci vetoed LD 284 in the 121st Legislature on the same grounds. The Constitution is not a partisan document. It is the foundation of our Republic and we must ensure that every law passed is in accordance with it.”

Jackson disagreed that the law was unconstitutional, instead suggesting that LePage was merely doing the bidding of large landowners who hire Canadian workers. In a statement released by the Senate Democratic Office, he accused LePage of being “more interested in giving jobs to Canadians rather than Maine workers.”

“The logging season is about to kick off and there are plenty of northern Mainers that are eager to work,” Jackson said. “The question I’d like to ask the governor is, ‘Whose side are you on?’ His veto sent the message that he’s on the side of our neighbors to the north.”

The bill, which passed the Legislature last month by the slimmest margin, is part of a broader debate about Canadian loggers working in the Maine woods. That debate has been simmering for decades but occasionally erupts onto the political scene during tough economic times.

In his explanation to lawmakers, LePage referred to a letter from Attorney General William Schneider stating that LD 340 raises pre-emption and equal protection issues under the federal Constitution.

Schneider wrote that bonded workers are approved after an elaborate process. Contractors are only permitted to use Canadian loggers if they cannot find Maine or U.S. workers.

“While the courts have allowed states to ban aliens from certain occupations — such as police officers — there seems to be no basis upon which to ban federally certified workers, particularly where the certification is based upon the unavailability of U.S. workers,” Schneider wrote.

But Jackson said in an interview Tuesday night that federal officials have told the state that Maine can legally choose not to participate in the bonded labor program for harvesting on state-owned land. The Allagash Democrat also questioned LePage’s commitment to enforcing the law by pointing out that the administration has delayed proceedings against two firms accused of violating the state’s rules on use of foreign laborers.

“It’s further evidence that he is for landowners bringing in foreign labor,” Jackson said. “It is clear in my mind.”

Will Harris, director of the Bureau of Parks and Lands, said the bureau makes it clear to contractors that they are not to use non-U.S. workers.

In the instance of the violation earlier this year, a contractor with multiple jobs in Maine transferred a bonded laborer — unknown to the bureau — from one site to the job on state-owned lands. The worker then was moved to another site after the bureau learned about the issue.

“I don’t think it is going to really change what we are doing,” Harris said of Jackson’s bill and LePage’s veto. “We are going to keep our current policy.”

While Harris said he is only aware of the single violation since becoming bureau director in 2007, Jackson suggested the problem is fairly common but is rarely reported.

There are still several logging-related bills pending in the Legislature that are likely to spark considerable discussion.