Big tech companies and their top executives have been outspoken this year about immigration reform, net neutrality, and data privacy–but tax reform is by far the most important policy fight for them in 2017. And their lobbying filings show it.

While most of the people who work at tech companies are not Trump supporters, the companies themselves could benefit hugely from the new tax code currently being proposed by the administration and GOP leadership in Congress.

Tech companies like Apple and Microsoft have for a long time balked at the 35% corporate tax the current tax code requires them to pay on worldwide profits returned to the U.S. To avoid paying, the companies have parked as much of their profit as possible in overseas subsidiaries in countries like Bermuda and Ireland, where tax rates are low.

The Big 5 tech companies–Apple, Alphabet, Amazon, Facebook, and Microsoft–currently have a combined $457 billion held in overseas subsidiaries. Apple holds more profits overseas than any other company, with Microsoft not far behind.

Zion Research Group estimates that U.S. companies in general have $2.8 trillion in profits parked in overseas affiliates.

Donald Trump campaigned on a promise of reforming the tax code, and part of that promise was giving corporations a chance to bring their overseas cash hoards home at a greatly reduced tax rate. A little more than a year after the election of Trump, a GOP-led tax reform package making its way through Congress. The House version of the tax bill was approved November 16, and the Senate version is heading for a crucial showdown vote on the Senate floor.