The 32-year-old – the world's highest paid athlete according to Forbes magazine – follows in the steps of Barcelona forward and Argentina star Lionel Messi, who was found guilty of the same offence last year although the sums involved were allegedly smaller.
If he too is put on trial and found guilty, he risks "a fine of at least 28 million" euros ($31.3 million) and could potentially be jailed for three-and-a-half years, the Gestha union of experts at Spain's Inland Revenue said in a statement.
Ronaldo is accused of "four crimes against the public treasury between 2011-14... which involves tax fraud of 14,768,897 euros ($16.5m, £12.9m)", Madrid's public prosecutor's office said in a statement.
"The accused took advantage of a company structure created in 2010 to hide income generated in Spain from his image rights from tax authorities, which is a 'voluntary' and 'conscious' breach of his fiscal obligations in Spain," it said.
Prosecutors accuse the Portugal international of evading tax via a shell company based in the British Virgin Islands and another in Ireland, known for its low corporate tax rate.
In addition, they say he only declared 11.5 million euros of Spanish-related income from 2011 to 2014, while what he really earned during that time was close to 43 million euros.
And finally, they accuse him of "voluntarily" refusing to include 28.4 million euros in income linked to the sale of his image rights for the 2015 to 2020 period to a Spanish company.
Ronaldo's lawyer said the four-time World Player of the Year was stunned by the accusations.
"It's a total surprise for the player who feels wronged, which gives me a special responsibility to speak in his name of his feeling of sadness and injustice," Antonio Lobo Xavier told Portuguese television.
"Ronaldo declared his income in relation to his image rights in 2014, which also included the three previous years."
In a television interview last month when it was revealed that tax authorities had sent a report to prosecutors on Ronaldo's alleged fiscal evasion, Ronaldo had said he was "very serene."
"I know these things will be resolved with the best decision, so I'm fine," he had said.
The football world in Spain has been rocked by charges of tax evasion or corruption pressed against some of its top stars.
Messi was sentenced to a 21-month jail sentence and 2.09-million-euro fine last year for tax fraud.
The prison term will be suspended as is common in Spain for first offences for non-violent crimes carrying a sentence of less than two years.
The 29-year-old and his father Jorge Horacio Messi were found guilty of using companies in Belize, Britain, Switzerland and Uruguay to avoid paying taxes on 4.16 million euros of Messi's income earned from his image rights from 2007-09.
The income related to Messi's image rights that was hidden includes endorsement deals with Danone, Adidas, Pepsi-Cola, Procter & Gamble and the Kuwait Food Company.
In its statement, Gestha said the most favourable scenario for Ronaldo would be that he is also given a 21-month prison sentence.
Former Barca defender Javier Mascherano also agreed a one-year suspended sentence with authorities for tax fraud last year.
Meanwhile Brazil star and Barcelona forward Neymar and his parents are due to stand trial for alleged corruption over his transfer from Santos in 2013.