On March 24, after years of delays and an earlier rejection by the Obama administration, the Trump administration approved TransCanada’s application to build the 1,200-mile cross-border Keystone pipeline. While labor is eager to start work on the Keystone XL pipeline following the Trump administration’s permit approval, opponents are promising court battles lasting several years as well as a possible on-the-ground battle, similar to the one that delayed the Dakota Access pipeline.

The decision came in January, after President Trump ordered the State Dept. to review its 2015 rejection of the line. Secretary of State Rex Tillerson, former CEO of Exxon Mobil, recused himself from the review and decision.

“The presidential permit is only one part of a web of federal, state and local permits that must be obtained prior to starting construction,” said Fred Jauss, a former attorney with the Federal Energy Regulatory Commission and currently an attorney with the law firm Dorsey & Whitney. “Other federal agencies, such as the Army Corps of Engineers, state regulatory commissions and even local planning boards, may have requirements that need to be fulfilled by Keystone prior to construction.”

Environmental groups, including the Sierra Club, have confirmed they will file suit against the decision, which was largely based on a National Environmental Policy Act review completed in 2014, when the price of oil was $100 a barrel. Crude oil dropped below $50 in March.

The biggest and lengthiest fight is likely to come in Nebraska, where the $8-billion line doesn’t yet have an approved route. Environmental groups successfully fought a previously proposed route because it crossed the state’s aquifer. The state’s public service commission is expected to take until September to review a revised route, submitted in February. If approved, TransCanada would have to initiate eminent domain proceedings against the 10% of landowners who have refused to work with the company. An earlier court decision prohibits TransCanada from taking that action before September.

“You’re looking at two to three years of legal challenges, at least,” said Jane Kleeb, president of the Bold Alliance, which led the first fight against the Nebraska route after the approval was announced.

The Indigenous Environmental Network, a group of Native Americans, have said they will mobilize along the Keystone XL route as they did along the Dakota Access Pipeline.

Despite the challenges, the decision is a “significant milestone,” according to Russ Girling, TransCanada president and CEO.

“There’s thousands of people that are just ready and itching to get to work,” Girling said at the White House announcement. Girling brought with him Sean McGarvey, president of the North America’s Building Trades Unions. “NABTU is excited its members’ livelihoods are not restrained by the strong arm of the federal government when building the world’s safest pipeline,” McGarvey said in a statement.

Representatives from Quanta Services, which will help to build the line, were also at the announcement. “It is too early for us to know the specific role that Quanta might play on the project or when construction could start,” the company said.

The pipeline would move up to 830,000 barrels of tar-sands oil per day to Steele City, Neb., from Hardisty, Alberta. It is the last leg of a pipeline that already goes to Port Arthur, Texas.

A Welspun representative attended the announcement, too. The India-based company provided some of the steel for the 36-in. pipe, which was manufactured long ago and is ready to be laid in place. Although Trump in January said the pipeline would be made with U.S. steel, he walked back that pledge in March.

Over its two-year construction period, the last portion of the line is expected to support 3,900 direct construction jobs and 42,100 construction-related jobs, according to the State Dept. When finished, the line is expected to support 35 permanent employees.