1. Taxes in focus: U.S. Treasury Secretary Steven Mnuchin says the Trump administration's sweeping tax reforms are likely to be delayed.

Speaking to the Financial Times, Mnuchin admitted the original timetable is "not realistic" after setbacks in negotiations with Congress over health care.

Speaking of taxes -- Tuesday is the final day to file 2016 U.S. tax returns with the IRS.

2. U.K. election: The pound swung wildly on Tuesday as U.K. Prime Minister Theresa May unexpectedly called a general election for June 8.

The pound dropped nearly 1% before the announcement, but recovered the lost ground as May spoke.

3. United grilling: United Airlines executives could face some tough questions during an analyst call at 10:30 a.m. ET.

The airline's reputation has taken a major hit after a passenger was dragged off a United flight when he refused to give up his seat.

United Continental Holdings (UAL), the airline's owner, reported its latest financial results on Monday.

It posted a 57% drop in profits, which was actually better than the 70% decline that Wall Street had forecast. The airline acknowledged it "needs to do a much better job" serving its customers.

United shares were up 1% in premarket trading.

4. Big earnings day: Goldman Sachs (GS), Bank of America (BAC), Harley-Davidson (HOG) and United Health (UEEC) will report their results before the opening bell.

IBM (IBM) and Yahoo (YHOO) will follow after the close.

Goldman is expected to report strong results Tuesday. The bank has enjoyed a 24% surge in its stock price since Trump's victory.

5. Global market overview: U.S. stock futures are lower.

European markets were mostly down in early trading, while Asian markets closed with mixed results.

The Dow Jones industrial average, the S&P 500 and the Nasdaq all closed 0.9% higher on Monday.

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6. Economics: The U.S. Census Bureau will release housing starts and building permits data at 7:30 a.m. ET.

The International Monetary Fund will publish its World Economic Outlook at 9 a.m. ET. It is the first forecast to be published since Trump took office.

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7. Coming this week:

Tuesday - U.S. Tax Day; United Airlines (UAL) analyst call, Goldman Sachs (GS), Bank of America (BAC) and IBM (IBM) report earnings
Wednesday - U.S. Crude oil inventories report, Morgan Stanley (MS), BlackRock (BLK), eBay (EBAY), American Express (AXP) publish results
Thursday - Mattel (MAT) earnings report
Friday - U.S. release of Samsung's (SSNLF) Galaxy S8