Fears of a so-called Brexit, or a departure of Britain from the European Union, are really heating up. The country holds a referendum on the issue on June 23, and recent polls have suggested a tight race, with some polls even giving the "leave" camp the lead.

This has caused European stocks to decline in recent weeks. The Brexit vote has investors scared about Europe's financial future, but fear creates opportunity for enterprising investors, and fear of a Brexit is no exception. We'll look at three high-dividend stocks that are entering bargain territory because of uncertainty over a Brexit. All three are compelling choices for investors looking to build their dividend-growth portfolios.

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1. GlaxoSmithKline (GSK) - Get Report

Shares of U.K.-based GlaxoSmithKline are down 4.5% in the past month, even though the company has made significant progress in its turnaround. In recent years, Glaxo has suffered from erosion of its bread-and-butter respiratory portfolio, specifically Advair. Due to the loss of patent protection and the entry of generic competitors, sales of Advair have declined. This forced Glaxo to reshuffle its portfolio.

In 2014, GlaxoSmithKline sold its huge oncology drug portfolio to Novartis for $16 billion. GlaxoSmithKline also purchased some of Novartis' vaccine portfolio, for $7 billion. The two companies also established a joint venture to collaborate on their consumer health care businesses.

The strategy being employed is diversification. GlaxoSmithKline believes it is better to focus on both vaccines and consumer health care going forward. Vaccines in particular present a lot of growth potential, particularly in emerging markets, and these two areas tend to be less risky than pharmaceuticals.

Investors should not be overly concerned about a potential Brexit because Glaxo is a diversified company. It has a global reach, offering its products in more than 150 markets worldwide. It also has a blended business model across pharmaceuticals, vaccines and consumer health care products. Pharmaceuticals represent 58% of its portfolio, with vaccines and consumer health care combining for the other 42%.

This strategy is bearing fruit. Glaxo's first-quarter organic revenue and earnings rose 8%, adjusted to exclude changes in currency values. The company generated $1.15 billion in new product sales from HIV products Tivicay and Triumeq, Meningitis vaccines and its respiratory portfolio.

Vaccine sales rose 14% last quarter, while consumer health products revenue rose 4%, led by strong performance of Flonase OTC.

Glaxo expects 10%-12% core earnings growth this year, not including changes in the value of currencies.

Meanwhile, investors can scoop up shares of GlaxoSmithKline for a dividend yield of 5.8%. Even though the company is in a difficult turnaround period, management has committed to maintaining the dividend this year and next year. By 2018, it is expected that Glaxo's earnings will recover substantially.

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2. BP (BP) - Get Report

Not only is BP getting hit by Brexit fears, but it also has to grapple with the massive decline in oil and gas prices. While BP has a lot to contend with, it is also a massive business. BP is one of the six oil and gas super majors.

Brent crude prices (which are the international benchmark for oil) are still at half the level from two years ago when they reached more than $110 a barrel -- despite the recent recovery in oil prices.

BP has a whopping 7.7% dividend yield, as its share price has crumbled during the commodity crash. Although sky-high dividend yields can be a precursor to a dividend cut, management has said the dividend is the top priority in the company's financial framework.

BP has maintained its dividend thus far largely thanks to asset sales, cost cuts and its large refining business. The company unloaded $10 billion of assets deemed noncritical to the future growth of the company. Since 2010, BP sold $75 billion in assets.

The company has also cut spending significantly to keep profits afloat. In 2015, BP's annual controllable cash costs in 2015 were $3.4 billion lower than in the year before. Those costs are on track to be close to $7 billion lower in 2017, the company has said.

Lastly, BP's refining unit has been a huge boost. As opposed to oil exploration and production, which is entirely reliant on a supportive commodity price, refining actually improves when oil prices decline. Falling oil prices reduce refining costs, and assuming demand remains steady, this meaningfully expands profit margins.

BP booked $7.5 billion in pretax profit from its downstream business last year, thanks to refining.

Still, BP depends a lot on its exploration and production businesses, which continue to weigh the company down. BP lost $6.5 billion last year. It goes without saying that losses like this are not sustainable. If conditions do not improve, the dividend is likely to be reduced.

So, the million-dollar question is: "What will happen to oil prices?" On the demand side, BP estimates global oil demand will increase by 1.4 billion barrels per day, which is above the historical average. On the other hand, supply has not been cut to the degree that would warrant significantly higher oil prices.

The good news is that with crude prices rallying approximately 50% from their February 2016 lows, it could give BP just enough breathing room to see the dividend survive the current crisis.

BP's average realized Brent crude price last quarter was $34 per barrel. With Brent crude now at $50, BP's fundamentals will likely improve this quarter and beyond.

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3. Unilever (UL) - Get Report

Unilever has had a bad week. Its shares have fallen 6.8%. The good news is that similar to GlaxoSmithKline and BP, Unilever is not overly reliant on the EU. Far from it; Unilever actually derives the majority of its sales from outside Europe.

In fact, Unilever generates 66% of its total sales from emerging markets such as India, China, Latin America and Africa.

The other reason to buy Unilever on Brexit fears is because the company has a balanced product portfolio. It manufactures consumer staples as well as food products, which is an advantage because food is a stable business with high margins.

Approximately 25% of Unilever's revenue is derived from food. Just a few of Unilever's popular food brands include Ben & Jerry's, Hellmann's, Lipton and Knorr. Among Unilever's staples products are Dove and Axe.

This strategy has worked very well for the company. Last year, Unilever's net sales increased 10%, due to a 7.1% increase in emerging-market sales. Moreover, Unilever's core earnings per share rose 14% last year.

Unilever's success continued into 2016. First-quarter organic sales rose 4.7%, thanks to 8.3% revenue growth in the emerging markets. And, Unilever raised its dividend by 6% in the first quarter.

As emerging markets grow their economies at faster rates than mature markets such as the U.S., Unilever is enjoying industry-leading growth rates. Management projects eurozone GDP to grow 1.6% this year and the economies of India and China to grow by 7.4% and 6.2%, respectively.

The company fully intends to continue investing in new markets to keep its growth on track. It can do this because it has the ability to raise extremely cheap capital. For example, earlier this year Unilever issued $1.6 billion of bonds. Of these, approximately $339 million will mature in April 2020, at a 0% interest rate.

The fact that Unilever can raise essentially free capital should be extremely accretive to earnings. It will not be difficult for the company to find opportunities with greater than 0% growth.

As a result, investors should expect Unilever to continue generating solid growth, and with its stock price taking a dip on Brexit fears, Unilever is an attractive consumer staples stock. Based on its recent share price, Unilever yields 3.1%.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.