Arthur Levitt, chairman of the Securities and Exchange Commission, should expect to be bombarded by e-mail from thousands of students this week.

A group called Students for a Free Tibet are urging him to stop a planned public share offering by PetroChina, the main operating subsidiary of China's biggest oil company.

The students are part of an extraordinary ad hoc coalition that has united left-leaning protest groups, trade unions and conservative national security types against the offering.

The effort suggests the activism that non-governmental organisations took to the Seattle meeting of the World Trade Organisation is spreading to the financial markets, with consequences for companies running controversial operations.

The students say their main concern over PetroChina is that the money the company aims to raise in the US capital markets will finance a pipeline across Tibet, entrenching Chinese control there. Their proposed e-rally before the head of the SEC, however, may have little impact. PetroChina's registration has been submitted to regulators and the company's roadshow for investors is under way.

Their allies in the coalition are worried about issues that range from the oil company's part in developing the oil industry in Sudan, where they fear it will help to finance a civil war against Christian separatists in the south, to the consequences of providing US capital to finance what they call global "bad actors".

"This is the first chance that everybody in this country has had to take money right out of Beijing's pockets, and we're going to make it as tough as we can for them," said Lhadon Tethong of Students for a Free Tibet.

The students have been joined by the AFL-CIO union federation, which has organised an anti-PetroChina roadshow to compete with the investor roadshow being organised in the US by Goldman Sachs. PetroChina is seeking to raise about Dollars 3.4bn, much less than originally expected and some fund managers say the disinvestment campaign may have played a role.

"The escalating controversy over the PetroChina IPO (initial public offering) is a harbinger of what is to come," said Roger Robinson, senior director of international economic affairs in former President Reagan's National Security Council.

He is among conservatives working to encourage Congress to prevent the US capital markets being used to raise money for entities deemed likely to hurt US national security interests or encourage serious human rights abuses.

Some legislators, including Republicans Michael Oxley and Spencer Bachus, have already written to Mr Levitt over the issue.

The campaign - which is also being directed towards states and others controlling big pension funds - had its roots in efforts to encourage big US pension funds to divest shares in Talisman, the Canadian oil company, because of its joint venture with PetroChina in Sudan. Since this campaign started Talisman shares have dropped sharply, and some fund managers have sold their holdings.

TIAA-CREF, the world's biggest pension fund system with Dollars 280bn of assets, and the California Public Employees Retirement System (Calpers), managing Dollars 170bn in assets, said they did not plan to invest in the offering.

Because of the Sudan disinvestment campaign, the company was restructured to leave PetroChina in charge of domestic holdings, and the parent - China National Petroleum Corporation - in charge of the foreign operations. The PetroChina documents state that CNPC's use of the proceeds will be held in a separate account and used only to reduced CNPC's borrowings and to fund employee retraining and severance programmes.

This "firewall", however, has not convinced the deal's opponents, including Congressman Bachus from Alabama. In a recent letter to the SEC chairman, Mr Bachus said: "PetroChina is assuming a large portion of the debts formerly owned by its parent, CNPC.

"There is no question that this will significantly increase CNPC's access to financing that would otherwise be unavailable to fund its foreign operations. Therefore, the direct transfer of funds and assumption of old CNPC debt will significantly and materially aid CNPC in that it will now be able to use its current or future revenues to finance its foreign operations."